Related
How do I determine if variable is undefined or null?
My code is as follows:
var EmpName = $("div#esd-names div#name").attr('class');
if(EmpName == 'undefined'){
// DO SOMETHING
};
<div id="esd-names">
<div id="name"></div>
</div>
But if I do this, the JavaScript interpreter halts execution.
You can use the qualities of the abstract equality operator to do this:
if (variable == null){
// your code here.
}
Because null == undefined is true, the above code will catch both null and undefined.
The standard way to catch null and undefined simultaneously is this:
if (variable == null) {
// do something
}
--which is 100% equivalent to the more explicit but less concise:
if (variable === undefined || variable === null) {
// do something
}
When writing professional JS, it's taken for granted that type equality and the behavior of == vs === is understood. Therefore we use == and only compare to null.
Edit again
The comments suggesting the use of typeof are simply wrong. Yes, my solution above will cause a ReferenceError if the variable doesn't exist. This is a good thing. This ReferenceError is desirable: it will help you find your mistakes and fix them before you ship your code, just like compiler errors would in other languages. Use try/catch if you are working with input you don't have control over.
You should not have any references to undeclared variables in your code.
Combining the above answers, it seems the most complete answer would be:
if( typeof variable === 'undefined' || variable === null ){
// Do stuff
}
This should work for any variable that is either undeclared or declared and explicitly set to null or undefined. The boolean expression should evaluate to false for any declared variable that has an actual non-null value.
if (variable == null) {
// Do stuff, will only match null or undefined, this won't match false
}
if (typeof EmpName != 'undefined' && EmpName) {
will evaluate to true if value is not:
null
undefined
NaN
empty string ("")
0
false
Probably the shortest way to do this is:
if(EmpName == null) { /* DO SOMETHING */ };
Here is proof:
function check(EmpName) {
if(EmpName == null) { return true; };
return false;
}
var log = (t,a) => console.log(`${t} -> ${check(a)}`);
log('null', null);
log('undefined', undefined);
log('NaN', NaN);
log('""', "");
log('{}', {});
log('[]', []);
log('[1]', [1]);
log('[0]', [0]);
log('[[]]', [[]]);
log('true', true);
log('false', false);
log('"true"', "true");
log('"false"', "false");
log('Infinity', Infinity);
log('-Infinity', -Infinity);
log('1', 1);
log('0', 0);
log('-1', -1);
log('"1"', "1");
log('"0"', "0");
log('"-1"', "-1");
// "void 0" case
console.log('---\n"true" is:', true);
console.log('"void 0" is:', void 0);
log(void 0,void 0); // "void 0" is "undefined"
And here are more details about == (source here)
BONUS: reason why === is more clear than == (look on agc answer)
jQuery attr() function returns either a blank string or the actual value (and never null or undefined). The only time it returns undefined is when your selector didn't return any element.
So you may want to test against a blank string. Alternatively, since blank strings, null and undefined are false-y, you can just do this:
if (!EmpName) { //do something }
Edited answer: In my opinion, you shouldn't use the function from my below old answer. Instead, you should probably know the type of your variable and use the according to check directly (for example, wondering if an array is empty? just do if(arr.length===0){} etc.). This answer doesn't even answer OP's question.
I've come to write my own function for this. JavaScript is weird.
It is usable on literally anything. (Note that this also checks if the variable contains any usable values. But since this information is usually also needed, I think it's worth posting). Please consider leaving a note.
function empty(v) {
let type = typeof v;
if (type === 'undefined') {
return true;
}
if (type === 'boolean') {
return !v;
}
if (v === null) {
return true;
}
if (v === undefined) {
return true;
}
if (v instanceof Array) {
if (v.length < 1) {
return true;
}
} else if (type === 'string') {
if (v.length < 1) {
return true;
}
if (v === '0') {
return true;
}
} else if (type === 'object') {
if (Object.keys(v).length < 1) {
return true;
}
} else if (type === 'number') {
if (v === 0) {
return true;
}
}
return false;
}
TypeScript-compatible.
This function should do exactly the same thing like PHP's empty() function (see RETURN VALUES)
Considers undefined, null, false, 0, 0.0, "0" {}, [] as empty.
"0.0", NaN, " ", true are considered non-empty.
The shortest and easiest:
if(!EmpName ){
// DO SOMETHING
}
this will evaluate true if EmpName is:
null
undefined
NaN
empty
string ("")
0
false
If the variable you want to check is a global, do
if (window.yourVarName) {
// Your code here
}
This way to check will not throw an error even if the yourVarName variable doesn't exist.
Example: I want to know if my browser supports History API
if (window.history) {
history.back();
}
How this works:
window is an object which holds all global variables as its properties, and in JavaScript it is legal to try to access a non-existing object property. If history doesn't exist then window.history returns undefined. undefined is falsey, so code in an if(undefined){} block won't run.
In JavaScript, as per my knowledge, we can check an undefined, null or empty variable like below.
if (variable === undefined){
}
if (variable === null){
}
if (variable === ''){
}
Check all conditions:
if(variable === undefined || variable === null || variable === ''){
}
Since you are using jQuery, you can determine whether a variable is undefined or its value is null by using a single function.
var s; // undefined
jQuery.isEmptyObject(s); // will return true;
s = null; // defined as null
jQuery.isEmptyObject(s); // will return true;
// usage
if(jQuery.isEmptyObject(s)){
alert('Either variable: s is undefined or its value is null');
}else{
alert('variable: s has value ' + s);
}
s = 'something'; // defined with some value
jQuery.isEmptyObject(s); // will return false;
I've just had this problem i.e. checking if an object is null.
I simply use this:
if (object) {
// Your code
}
For example:
if (document.getElementById("enterJob")) {
document.getElementById("enterJob").className += ' current';
}
You can simply use the following (I know there are shorter ways to do this, but this may make it easier to visually observe, at least for others looking at the code).
if (x === null || x === undefined) {
// Add your response code here, etc.
}
source: https://www.growthsnippets.com/how-can-i-determine-if-a-variable-is-undefined-or-null/
jQuery check element not null:
var dvElement = $('#dvElement');
if (dvElement.length > 0) {
// Do something
}
else{
// Else do something else
}
With the newest javascript changes, you can use the new logical operator ??= to check if the left operand is null or undefined and if so assign the value of right operand.
SO,
if(EmpName == null){ // if Variable EmpName null or undefined
EmpName = 'some value';
};
Is equivalent to:
EmpName ??= 'some value';
The easiest way to check is:
if(!variable) {
// If the variable is null or undefined then execution of code will enter here.
}
I run this test in the Chrome console. Using (void 0) you can check undefined:
var c;
undefined
if (c === void 0) alert();
// output = undefined
var c = 1;
// output = undefined
if (c === void 0) alert();
// output = undefined
// check c value c
// output = 1
if (c === void 0) alert();
// output = undefined
c = undefined;
// output = undefined
if (c === void 0) alert();
// output = undefined
With the solution below:
const getType = (val) => typeof val === 'undefined' || !val ? null : typeof val;
const isDeepEqual = (a, b) => getType(a) === getType(b);
console.log(isDeepEqual(1, 1)); // true
console.log(isDeepEqual(null, null)); // true
console.log(isDeepEqual([], [])); // true
console.log(isDeepEqual(1, "1")); // false
etc...
I'm able to check for the following:
null
undefined
NaN
empty
string ("")
0
false
To test if a variable is null or undefined I use the below code.
if(typeof sVal === 'undefined' || sVal === null || sVal === ''){
console.log('variable is undefined or null');
}
if you create a function to check it:
export function isEmpty (v) {
if (typeof v === "undefined") {
return true;
}
if (v === null) {
return true;
}
if (typeof v === "object" && Object.keys(v).length === 0) {
return true;
}
if (Array.isArray(v) && v.length === 0) {
return true;
}
if (typeof v === "string" && v.trim().length === 0) {
return true;
}
return false;
}
(null == undefined) // true
(null === undefined) // false
Because === checks for both the type and value. Type of both are different but value is the same.
Let's look at this,
let apple; // Only declare the variable as apple
alert(apple); // undefined
In the above, the variable is only declared as apple. In this case, if we call method alert it will display undefined.
let apple = null; /* Declare the variable as apple and initialized but the value is null */
alert(apple); // null
In the second one it displays null, because variable of apple value is null.
So you can check whether a value is undefined or null.
if(apple !== undefined || apple !== null) {
// Can use variable without any error
}
The foo == null check should do the trick and resolve the "undefined OR null" case in the shortest manner. (Not considering "foo is not declared" case.) But people who are used to have 3 equals (as the best practice) might not accept it. Just look at eqeqeq or triple-equals rules in eslint and tslint...
The explicit approach, when we are checking if a variable is undefined or null separately, should be applied in this case, and my contribution to the topic (27 non-negative answers for now!) is to use void 0 as both short and safe way to perform check for undefined.
Using foo === undefined is not safe because undefined is not a reserved word and can be shadowed (MDN). Using typeof === 'undefined' check is safe, but if we are not going to care about foo-is-undeclared case the following approach can be used:
if (foo === void 0 || foo === null) { ... }
You can do something like this, I think its more efficient for multiple value check on the same variable in one condition
const x = undefined;
const y = null;
const z = 'test';
if ([undefined, null].includes(x)) {
// Will return true
}
if ([undefined, null].includes(y)) {
// Will return true
}
if ([undefined, null].includes(z)) {
// Will return false
}
No one seems to have to posted this yet, so here we go:
a?.valueOf() === undefined works reliably for either null or undefined.
The following works pretty much like a == null or a == undefined, but it could be more attractive for purists who don't like == 😎
function check(a) {
const value = a?.valueOf();
if (value === undefined) {
console.log("a is null or undefined");
}
else {
console.log(value);
}
}
check(null);
check(undefined);
check(0);
check("");
check({});
check([]);
On a side note, a?.constructor works too:
function check(a) {
if (a?.constructor === undefined) {
console.log("a is null or undefined");
}
}
check(null);
check(undefined);
check(0);
check("");
check({});
check([]);
Calling typeof null returns a value of “object”, as the special value null is considered to be an empty object reference. Safari through version 5 and Chrome through version 7 have a quirk where calling typeof on a regular expression returns “function” while all other browsers return “object”.
var x;
if (x === undefined) {
alert ("only declared, but not defined.")
};
if (typeof y === "undefined") {
alert ("not even declared.")
};
You can only use second one: as it will check for both definition and declaration
var i;
if (i === null || typeof i === 'undefined') {
console.log(i, 'i is undefined or null')
}
else {
console.log(i, 'i has some value')
}
I still think the best/safe way to test these two conditions is to cast the value to a string:
var EmpName = $("div#esd-names div#name").attr('class');
// Undefined check
if (Object.prototype.toString.call(EmpName) === '[object Undefined]'){
// Do something with your code
}
// Nullcheck
if (Object.prototype.toString.call(EmpName) === '[object Null]'){
// Do something with your code
}
I'm using AngularJS ver. 1.2.15 on my project. And, I have a select element on one of my views as per below:
<select class="select-white form-control form-select" id="cat2_{{feed.id}}" ng-model="feed.operationstatusid" ng-change="updateCategoryAndStatus(feed, true)"></select>
And, I'm feeding this element like this:
function SetCategory2(cat1Id, feed) {
var feedId = feed.id;
var fromRuleOpStatusId = -1;
$('#cat2_' + feedId).find('option').remove();
if (cat1Id > -1) {
$('#cat2_' + feedId).append($('<option></option>').text(lang.SelectSubCategory).val(0));
$.each($scope.category2, function (index, cat2Item) {
$('#cat2_' + feedId).append($('<option></option>').text(cat2Item.statusdescription).val(cat2Item.id));
});
var isselected = false;
$.each($scope.category2, function (index, cat2Item) {
if (feed.operationstatusid == cat2Item.id) {
$('#cat2_' + feedId).val(cat2Item.id);
fromRuleOpStatusId = -1;
isselected = true;
}
else {
var feedStr = "";
if (feed.title != undefined && feed.title != null) {
feedStr = feed.title.toLowerCase();
}
if ($scope.catTitleRulesTwo) {
$.each($scope.catTitleRulesTwo, function (r_index, r_item) {
if (cat2Item.id == r_item.titleCode && !isselected) {
if (feedStr != undefined && feedStr != null && r_item != undefined && r_item != null) {
String.prototype.contains = function (str) { return this.toLowerCase().indexOf(str) !== -1; };
var text = feedStr;
if (eval(r_item.ruleexpression)) {
$('#cat2_' + feedId).val(cat2Item.id);
fromRuleOpStatusId = cat2Item.id;
isselected = true;
}
}
}
});
}
}
});
if (fromRuleOpStatusId != -1) {
feed.operationstatusid = fromRuleOpStatusId;
}
}
else {
$('#cat2_' + feedId).append($('<option></option>').text(lang.SelectSubCategory).val(0));
}
}
I am aware of the facts about eval function, but the project I'm working on is quite old, so does the code. Anyway, this is about business logic and quite irrelevant with the thing I'm going to ask (or so I was thinking).
As you can see I'm appending all the options before I set the value of the selectbox with using .val(...). I have also checked that values do match along with the data types. But, when I observe this function step by step, I saw that selected value does show up without flaw. After the code finish with my above mentioned function (SetCategory2), code goes through on of the function located on AngularJS file, named xhr.onreadystatechange. It's not a long function, so I'm sharing it also on below.
xhr.onreadystatechange = function() {
if (xhr && xhr.readyState == 4) {
var responseHeaders = null,
response = null;
if(status !== ABORTED) {
responseHeaders = xhr.getAllResponseHeaders();
response = ('response' in xhr) ? xhr.response : xhr.responseText;
}
completeRequest(callback,
status || xhr.status,
response,
responseHeaders);
}
};
After the code released from this function, respective selectbox's value is pointed at the empty option.
I have run into topics which talks about this behaviour might due to invalid option-value match, but as I described above, I append all my options before deciding the value. So, I can't figure out what I'm missing.
Thank you in advance.
Why does HTML5 validation fail when having duplicate element IDs but on different <template>. I'm planning to use only one template at a time so the actual DOM ID won't be duplicated.
something like:
<template id="companyAccount">
<li><label>Company: <input type="text" id="account_name"></label></li>
<li><label>Street: <input id="account_street" ...
...
</template>
<template id="residentialAccount">
<li><label>Name: <input type="text" id="account_name"></label></li>
<li><label>Street: <input id="account_street" ...
...
</template>
<script>
...
let template = $(isResidential ? '#residentialAccount' : '#companyAccount').get(0).content;
$('#account_info').empty().append(template.cloneNode(true));
</script>
As TJBlackman mentioned each value for id attributes must be unique. However when working with code it's up to you to determine if the code being imported contains a duplicate id. Additionally I've pretty much stopped using validators for the most part as they aren't well maintained (and the W3C's CSS validator is atrocious) and the consoles, proper error handling and using the XML parser for HTML5 will tell you pretty much everything you need to know.
You have a couple of options. You can use data-account="residential" (don't make the mistake of using camelCasing as that will eventually put you in direct conflict with the standards bodies) and detect the attribute via document.querySelectorAll:
function $(o)
{
var a = true;
try {document.querySelectorAll(o);}
catch(err) {a = false; console.log('Error: "'+o+'" is not a valid CSS selector.'); sound.notice();}
return (a && document.querySelectorAll && document.querySelectorAll(o)) ? document.querySelectorAll(o) : false;
}
Usage: $('[data-account="residential"]')[0].length and $('[data-account="residential"]')[0].value.
Alternatively you can do what I do with my platform which has things tightly integrated though this is the function I use that you might decide to slim down for your specific purposes. You can use document.createTreeWalker and literally go through every single element to scan for walker.currentNode.hasAttribute('id') to test against document.getElementById. This code is used before importing XML in to the DOM on my platform:
/******** part of larger ajax() function ********/
if (xhr.readyState == 4 && xhr.status != 204)
{}
//This code occurs within the above condition.
var r = jax_id_duplication_prevention(xhr.responseXML,param_id_container_pos,id_container);
if (r)
{
if (param_id_container_pos=='after') {id_container.parentNode.insertBefore(xml.getElementsByTagName('*')[0],id_container.nextSibling);}
else if (param_id_container_pos=='before') {id_container.parentNode.insertBefore(document.importNode(xml.getElementsByTagName('*')[0],true),id_container);}
else if (param_id_container_pos=='first')
{
if (id_container.childNodes.length > 0) {id_container.insertBefore(document.importNode(xml.getElementsByTagName('*')[0],true),id_container.firstChild);}
else {id_container.appendChild(document.importNode(xml.getElementsByTagName('*')[0],true));}
}
else if (param_id_container_pos=='inside') {id_container.appendChild(document.importNode(xml.getElementsByTagName('*')[0],true));}
else if (param_id_container_pos=='replace') {id_container.parentNode.replaceChild(document.importNode(xml.getElementsByTagName('*')[0],true),id_container);}
else if (param_id_container_pos=='fragment')
{
if (option.fragment) {delete option.fragment;}
option.fragment = document.importNode(new DOMParser().parseFromString(xhr.responseText,'application/xml').childNodes[0],true);
if (id_container && typeof id_container == 'function') {id_container();}
}
else {alert('Error: unknown position to import data to: '+id_container_pos);}
}
/******** part of larger ajax() function ********/
function ajax_id_duplication_prevention(xml,param_id_container_pos,id_container)
{
var re = true;
if (typeof id_container == 'string' && id_container.length > 0 && id_(id_container)) {id_container = id_(id_container);}
if (typeof option.id_fade == 'string' && option.id_fade.length > 0 && id_(option.id_fade)) {element_del(option.id_fade); option.id_fade = '';}
if (typeof xml.firstChild.hasAttribute == 'function')
{
if (xml.firstChild.hasAttribute('id') && xml.firstChild.getAttribute('id').length > 0 && id_(xml.firstChild.getAttribute('id')) && id_(xml.firstChild.id).parentNode.id=='liquid') {change(xml.firstChild.id,'fade');}
if (xml.firstChild.hasAttribute('id') && xml.firstChild.getAttribute('id').length > 0 && id_(xml.firstChild.id) && !id_(xml.firstChild.id).parentNode.id=='liquid') {re = false;}
else if (typeof document.createTreeWalker=='function')
{
var idz = [];
try
{
var walker = document.createTreeWalker(xml,NodeFilter.SHOW_ELEMENT,null,false);
while (walker.nextNode())
{
if (walker.currentNode.hasAttribute('id') && walker.currentNode.getAttribute('id').length > 0)
{
if (walker.currentNode.id==undefined && walker.currentNode.nodeName.toLowerCase()=='parsererror') {console.log('Error: a parser error was detected.');}
else if (walker.currentNode.id==undefined) {alert('walker.currentNode.nodeName = '+walker.currentNode.nodeName+'\n\n'+document.serializeToString(xml));}
else
{
for (var i = 0; i<id_('liquid').childNodes.length; i++)
{
if (id_('liquid').childNodes[i].nodeType==1 && id_(walker.currentNode.id) && is_node_parent(walker.currentNode.id,id_('liquid').childNodes[i]) && (param_id_container_pos!='replace' || walker.currentNode.id!=id_container.id))
{
if (param_id_container_pos != 'replace' && id_container != walker.currentNode.id) {element_del(id_('liquid').childNodes[i]);}//If changing operator test: ajax('get','?ajax=1&web3_url=/'+url_section()+'/'+url_page(),'replace',push_current_id());
}
}
var n = id_(walker.currentNode.id);
if (in_array(walker.currentNode.id,idz))
{
var fd = new FormData();
fd.append('ajax','error_xml');
fd.append('post_error','Duplicate id <code>'+walker.currentNode.id+'</code>.');
fd.append('post_url',url_window().split(url_base())[1].split('?')[0]);
fd.append('post_xml',new XMLSerializer().serializeToString(xml));
if (fd) {ajax('post',path+'/themes/',fd);}
modal.alert('Error: can not import XML, the id \''+walker.currentNode.id+'\' was detected twice in the layer being imported. Duplicated ID\'s break expected functionality and are illegal. While the XML content was not imported it is still possible that the related request was successful. It is possible to override this problem by simply doing a full request (press the Go button in your browser\'s graphic user interface) however if the id is referenced programmatically the website may exhibit unusual behavior.');
break;
setTimeout(function()
{
history.back();
push_reload();
console.log('Developer: duplicate id '+walker.currentNode.id+' was encounterted.');
if (status >= 9) {modal.xml('Duplicate ID Error', '%3Cp%3EError%3A%20the%20id%20%3Ccode%3E'+walker.currentNode.id+'%3C%2Fcode%3E%20occurred%20twice%20and%20therefore%20the%20page%20can%20not%20be%20viewed.%3C%2Fp%3E%3Cp%3EFor%20debugging%20and%20fixing%20purposes%20you%20should%20consider%20opening%20the%20URL%20in%20a%20new%20tab.%3C%2Fp%3E%3Cdiv%20class%3D%22center%20margin%22%3E%3Cinput%20onclick%3D%22modal.close()%3B%22%20tabindex%3D%223%22%20type%3D%22button%22%20value%3D%22Close%22%20%2F%3E%3C%2Fdiv%3E');}
else {modal.xml('Duplicate ID Error', '%3Cp%3EError%3A%20the%20id%20%3Ccode%3E'+walker.currentNode.id+'%3C%2Fcode%3E%20occurred%20twice%20and%20therefore%20the%20page%20can%20not%20be%20viewed.%3C%2Fp%3E%3Cdiv%20class%3D%22center%20margin%22%3E%3Cinput%20onclick%3D%22modal.close()%3B%22%20tabindex%3D%223%22%20type%3D%22button%22%20value%3D%22Close%22%20%2F%3E%3C%2Fdiv%3E');}
re = false;
},4000);
}
else {idz.push(walker.currentNode.id);}
}
if (id_(walker.currentNode.id) && (param_id_container_pos!='replace' && walker.currentNode.id!=id_container.id && !is_node_parent(walker.currentNode.id,id_container)))
{//ajax replace (carousel loader) complications if changed.
re = false;
modal.alert('Error: unable to import page, the id \''+walker.currentNode.id+'\' already exists in the DOM.');
break;
}
}
}
}
catch (err) {}//IE9
}
}
return re;
}
Regardless of how you approach addressing the issue it is not one addressed by the standards bodies and must be explicitly handled by developers. Failure to handle duplicate id attribute/values will result in the wrong element being chosen at some point which may quietly accrue compromised/malformed data over time that no one might notice for years and thus could easily hinder if not outright destroy any business relations effected by it. Good luck!
This question already has answers here:
How do I test for an empty JavaScript object?
(48 answers)
Closed 5 years ago.
What is the fastest way to check if an object is empty or not?
Is there a faster and better way than this:
function count_obj(obj){
var i = 0;
for(var key in obj){
++i;
}
return i;
}
For ECMAScript5 (not supported in all browsers yet though), you can use:
Object.keys(obj).length === 0
I'm assuming that by empty you mean "has no properties of its own".
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isEmpty(obj) {
// null and undefined are "empty"
if (obj == null) return true;
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// If it isn't an object at this point
// it is empty, but it can't be anything *but* empty
// Is it empty? Depends on your application.
if (typeof obj !== "object") return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
}
Examples:
isEmpty(""), // true
isEmpty(33), // true (arguably could be a TypeError)
isEmpty([]), // true
isEmpty({}), // true
isEmpty({length: 0, custom_property: []}), // true
isEmpty("Hello"), // false
isEmpty([1,2,3]), // false
isEmpty({test: 1}), // false
isEmpty({length: 3, custom_property: [1,2,3]}) // false
If you only need to handle ECMAScript5 browsers, you can use Object.getOwnPropertyNames instead of the hasOwnProperty loop:
if (Object.getOwnPropertyNames(obj).length > 0) return false;
This will ensure that even if the object only has non-enumerable properties isEmpty will still give you the correct results.
EDIT: Note that you should probably use ES5 solution instead of this since ES5 support is widespread these days. It still works for jQuery though.
Easy and cross-browser way is by using jQuery.isEmptyObject:
if ($.isEmptyObject(obj))
{
// do something
}
More: http://api.jquery.com/jQuery.isEmptyObject/
You need jquery though.
Underscore and lodash each have a convenient isEmpty() function, if you don't mind adding an extra library.
_.isEmpty({});
Lets put this baby to bed; tested under Node, Chrome, Firefox and IE 9, it becomes evident that for most use cases:
(for...in...) is the fastest option to use!
Object.keys(obj).length is 10 times slower for empty objects
JSON.stringify(obj).length is always the slowest (not surprising)
Object.getOwnPropertyNames(obj).length takes longer than Object.keys(obj).length can be much longer on some systems.
Bottom line performance wise, use:
function isEmpty(obj) {
for (var x in obj) { return false; }
return true;
}
or
function isEmpty(obj) {
for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }
return true;
}
Results under Node:
first result: return (Object.keys(obj).length === 0)
second result: for (var x in obj) { return false; }...
third result: for (var x in obj) { if (obj.hasOwnProperty(x)) return false; }...
forth result: return ('{}' === JSON.stringify(obj))
Testing for Object with 0 keys
0.00018
0.000015
0.000015
0.000324
Testing for Object with 1 keys
0.000346
0.000458
0.000577
0.000657
Testing for Object with 2 keys
0.000375
0.00046
0.000565
0.000773
Testing for Object with 3 keys
0.000406
0.000476
0.000577
0.000904
Testing for Object with 4 keys
0.000435
0.000487
0.000589
0.001031
Testing for Object with 5 keys
0.000465
0.000501
0.000604
0.001148
Testing for Object with 6 keys
0.000492
0.000511
0.000618
0.001269
Testing for Object with 7 keys
0.000528
0.000527
0.000637
0.00138
Testing for Object with 8 keys
0.000565
0.000538
0.000647
0.00159
Testing for Object with 100 keys
0.003718
0.00243
0.002535
0.01381
Testing for Object with 1000 keys
0.0337
0.0193
0.0194
0.1337
Note that if your typical use case tests a non empty object with few keys, and rarely do you get to test empty objects or objects with 10 or more keys, consider the Object.keys(obj).length option. - otherwise go with the more generic (for... in...) implementation.
Note that Firefox seem to have a faster support for Object.keys(obj).length and Object.getOwnPropertyNames(obj).length, making it a better choice for any non empty Object, but still when it comes to empty objects, the (for...in...) is simply 10 times faster.
My 2 cents is that Object.keys(obj).length is a poor idea since it creates an object of keys just to count how many keys are inside, than destroys it! In order to create that object he needs to loop overt the keys... so why use it and not the (for... in...) option :)
var a = {};
function timeit(func,count) {
if (!count) count = 100000;
var start = Date.now();
for (i=0;i<count;i++) func();
var end = Date.now();
var duration = end - start;
console.log(duration/count)
}
function isEmpty1() {
return (Object.keys(a).length === 0)
}
function isEmpty2() {
for (x in a) { return false; }
return true;
}
function isEmpty3() {
for (x in a) { if (a.hasOwnProperty(x)) return false; }
return true;
}
function isEmpty4() {
return ('{}' === JSON.stringify(a))
}
for (var j=0;j<10;j++) {
a = {}
for (var i=0;i<j;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4);
}
a = {}
for (var i=0;i<100;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1);
timeit(isEmpty2);
timeit(isEmpty3);
timeit(isEmpty4, 10000);
a = {}
for (var i=0;i<1000;i++) a[i] = i;
console.log('Testing for Object with '+Object.keys(a).length+' keys')
timeit(isEmpty1,10000);
timeit(isEmpty2,10000);
timeit(isEmpty3,10000);
timeit(isEmpty4,10000);
Elegant way - use keys
var myEmptyObj = {};
var myFullObj = {"key":"value"};
console.log(Object.keys(myEmptyObj).length); //0
console.log(Object.keys(myFullObj).length); //1
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
function isEmpty( o ) {
for ( var p in o ) {
if ( o.hasOwnProperty( p ) ) { return false; }
}
return true;
}
var x= {}
var y= {x:'hi'}
console.log(Object.keys(x).length===0)
console.log(Object.keys(y).length===0)
true
false
http://jsfiddle.net/j7ona6hz/1/
Surprised to see so many weak answers on such a basic JS question... The top answer is no good too for these reasons:
it generates a global variable
returns true on undefined
uses for...in which is extremely slow by itself
function inside for...in is useless - return false without hasOwnProperty magic will work fine
In fact there's a simpler solution:
function isEmpty(value) {
return Boolean(value && typeof value === 'object') && !Object.keys(value).length;
}
https://lodash.com/docs#isEmpty comes in pretty handy:
_.isEmpty({}) // true
_.isEmpty() // true
_.isEmpty(null) // true
_.isEmpty("") // true
How bad is this?
function(obj){
for(var key in obj){
return false; // not empty
}
return true; // empty
}
No need for a library.
function(){ //must be within a function
var obj = {}; //the object to test
for(var isNotEmpty in obj) //will loop through once if there is a property of some sort, then
return alert('not empty')//what ever you are trying to do once
return alert('empty'); //nope obj was empty do this instead;
}
It might be a bit hacky. You can try this.
if (JSON.stringify(data).length === 2) {
// Do something
}
Not sure if there is any disadvantage of this method.
fast onliner for 'dictionary'-objects:
function isEmptyDict(d){for (var k in d) return false; return true}
You can write a fallback if Array.isArray and Object.getOwnPropertyNames is not available
XX.isEmpty = function(a){
if(Array.isArray(a)){
return (a.length==0);
}
if(!a){
return true;
}
if(a instanceof Object){
if(a instanceof Date){
return false;
}
if(Object.getOwnPropertyNames(a).length == 0){
return true;
}
}
return false;
}
Imagine you have the objects below:
var obj1= {};
var obj2= {test: "test"};
Don't forget we can NOT use === sign for testing an object equality as they get inheritance, so If you using ECMA 5 and upper version of javascript, the answer is easy, you can use the function below:
function isEmpty(obj) {
//check if it's an Obj first
var isObj = obj !== null
&& typeof obj === 'object'
&& Object.prototype.toString.call(obj) === '[object Object]';
if (isObj) {
for (var o in obj) {
if (obj.hasOwnProperty(o)) {
return false;
break;
}
}
return true;
} else {
console.error("isEmpty function only accept an Object");
}
}
so the result as below:
isEmpty(obj1); //this returns true
isEmpty(obj2); //this returns false
isEmpty([]); // log in console: isEmpty function only accept an Object
funtion isEmpty(o,i)
{
for(i in o)
{
return!1
}
return!0
}
here's a good way to do it
function isEmpty(obj) {
if (Array.isArray(obj)) {
return obj.length === 0;
} else if (typeof obj === 'object') {
for (var i in obj) {
return false;
}
return true;
} else {
return !obj;
}
}
var hasOwnProperty = Object.prototype.hasOwnProperty;
function isArray(a) {
return Object.prototype.toString.call(a) === '[object Array]'
}
function isObject(a) {
return Object.prototype.toString.call(a) === '[object Object]'
}
function isEmpty(a) {
if (null == a || "" == a)return!0;
if ("number" == typeof a || "string" == typeof a)return!1;
var b = !0;
if (isArray(a)) {
if (!a.length)return!0;
for (var c = 0; c < a.length; c++)isEmpty(a[c]) || (b = !1);
return b
}
if (isObject(a)) {
for (var d in a)hasOwnProperty.call(a, d) && (isEmpty(a[d]) || (b = !1));
return b
}
return!0
}
May be you can use this decision:
var isEmpty = function(obj) {
for (var key in obj)
if(obj.hasOwnProperty(key))
return false;
return true;
}
I modified Sean Vieira's code to suit my needs. null and undefined don't count as object at all, and numbers, boolean values and empty strings return false.
'use strict';
// Speed up calls to hasOwnProperty
var hasOwnProperty = Object.prototype.hasOwnProperty;
var isObjectEmpty = function(obj) {
// null and undefined are not empty
if (obj == null) return false;
if(obj === false) return false;
if(obj === true) return false;
if(obj === "") return false;
if(typeof obj === "number") {
return false;
}
// Assume if it has a length property with a non-zero value
// that that property is correct.
if (obj.length > 0) return false;
if (obj.length === 0) return true;
// Otherwise, does it have any properties of its own?
// Note that this doesn't handle
// toString and valueOf enumeration bugs in IE < 9
for (var key in obj) {
if (hasOwnProperty.call(obj, key)) return false;
}
return true;
};
exports.isObjectEmpty = isObjectEmpty;
here my solution
function isEmpty(value) {
if(Object.prototype.toString.call(value) === '[object Array]') {
return value.length == 0;
} else if(value != null && typeof value === 'object') {
return Object.getOwnPropertyNames(value).length == 0;
} else {
return !(value || (value === 0));
}
}
Chears
if (Object.getOwnPropertyNames(obj1).length > 0)
{
alert('obj1 is empty!');
}
Can someone help explain the logic used in the JavaScript code here?
The code below checks to see if two strings are anagrams of each other, but I don't understand the method being used to check the string.
Thanks.
<script type="text/javascript">
$(document).ready(function() {
var anagram = function(str1, str2){
if (str1.length !== str2.length) {
return false;
}
var sortstr1 = str1.split('').sort().join('');
var sortstr2 = str2.split('').sort().join('');
return (sortstr1 === sortstr2);
}
$('.AnagramChecker').on('click', function(e) {
e.preventDefault();
if($('#string1').val() == '') {
$('#string1').addClass('error');
if($('#string2').val() == '') {
$('#string2').addClass('error');
}
$('.results').empty();
$('.results').hide();
} else {
$('#string1').removeClass('error');
if($('#string2').val() == '') {
$('#string2').addClass('error');
$('.results').empty();
$('.results').hide();
} else {
$('#string2').removeClass('error');
var isAnagram = anagram($('#string1').val(), $('#string2').val());
$('#string1').val('');
$('#string2').val('')
$('.results').show();
$('.results').empty().append('Anagram is: ' + isAnagram);
}
}
});
});
</script>
Both strings are being split down into arrays of their individual characters, which are then sorted alphabetically and joined again into strings. The strings are then compared, and if they are the same, are anagrams of one another.
function anagrams(str1,str2){
//spliting string into array
let arr1 = str1.split("");
let arr2 = str2.split("");
//verifying array lengths
if(arr1.length !== arr2.length){
return false;
}
//creating objects
let frqcounter1={};
let frqcounter2 ={};
// looping through array elements and keeping count
for(let val of arr1){
frqcounter1[val] =(frqcounter1[val] || 0) + 1;
}
for(let val of arr2){
frqcounter2[val] =(frqcounter2[val] || 0) + 1;
}
console.log(frqcounter1);
console.log(frqcounter2);
//loop for every key in first object
for(let key in frqcounter1){
//if second object does not contain same frq count
if(frqcounter2[key] !== frqcounter1[key]){
return false;
}
}
return true;
}
anagrams('anagrams','nagramas');
function compare(a1,a2){
if(a1.length != a2.length){
return false
}
var f1 = {}, f2 ={};
for(var a of a1){
f1[a] = ++f1[a] || 1
}
for(var a of a2){
f2[a] = ++f2[a] || 1
}
for(var key in f1){
if(!(key in f2)){
return false
}
if(f1[key] != f2[key]) {
return false
}
}
return true
}