Unable to get the length of JSON object - json

Question

I am getting 'TypeError: Cannot convert undefined or null to object' while trying to access the length of json object in nodejs.
Following is how my data looks like:
{
"college": [
{
"colleges": [],
"department": [
1,
2,
3
],
"general_course": [],
"id": 1,
"name": "College of the Arts",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1919"
},
{
"colleges": [],
"department": [
4,
5,
6
],
"general_course": [],
"id": 2,
"name": "College of Communications",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1920"
},
{
"colleges": [],
"department": [
7,
12
],
"general_course": [],
"id": 3,
"name": "College of Education",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1921"
},
{
"colleges": [],
"department": [
13,
17,
19
],
"general_course": [],
"id": 4,
"name": "College of Engineering and Computer Science",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1922"
},
{
"colleges": [],
"department": [
20,
26,
27
],
"general_course": [],
"id": 5,
"name": "College of Health and Human Development",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1923"
},
{
"colleges": [],
"department": [
28,
29,
32,
48
],
"general_course": [],
"id": 6,
"name": "College of Humanities and Social Sciences",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1924"
},
{
"colleges": [],
"department": [
52,
57
],
"general_course": [],
"id": 7,
"name": "College of Natural Sciences and Mathematics",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1925"
},
{
"colleges": [],
"department": [
58,
59,
63
],
"general_course": [],
"id": 8,
"name": "Mihaylo College of Business and Economics",
"short_name": "",
"url": "/content.php?catoid=16&navoid=1926"
}
]
}
Step 1 - Parsing it into nodejs:
let colleges = JSON.parse(data)
Step 2 - Saving it into the dialogflow app data:
app.data.collegeData = data;
Step 3 - Accessing the length:
let collegeLength = Object.keys(app.data.collegeData.college).length;
Getting following error in firebase console:
TypeError: Cannot convert undefined or null to object
Update:
Here is the code:
if ( app.data.collegeData === undefined ){
app.data.collegeData = [];
}
**Step 1 =>**
showColleges(college);
**Step 2 =>**
function showColleges(collegeName){
if (app.data.collegeData.length === 0){
getCollegeData().then(buildSingleCollegeResponse(collegeName))
.catch(function (err){
console.log('No college data')
console.log(err)
});
}
else{
buildSingleCollegeResponse(collegeName);
}
}
**Step 3 =>**
function getCollegeData(){
console.log('Inside get College Data')
return requestAPI(URL)
.then(function (data) {
let colleges = JSON.parse(data)
if (colleges.hasOwnProperty('college')){
saveData(colleges)
}
return null;
})
.catch(function (err) {
console.log('No college data')
console.log(err)
});
}
**Step 4 =>**
function saveData(data){
app.data.collegeData = data;
console.log(app.data.collegeData)
}
**Step 5 =>**
function buildSingleCollegeResponse(collegeName){
let responseToUser, text;
//console.log('Data is -> '+ Object.keys(app.data.collegeData.college).length);
//console.log('Length is -> '+ app.data.collegeData.college.length);
console.log('Count is -> '+app.data.collegeCount);
let collegeLength = Object.keys(app.data.collegeData.college).length;
if ( collegeLength === 0){
responseToUser = 'No colleges available at this time';
text = 'No colleges available at this time';
}
else if ( app.data.collegeCount < collegeLength ){
for ( var i = 1; i <= collegeLength; i++)
{
console.log('All Colleges:: '+app.data.collegeData.college[i])
let coll = app.data.collegeData.college[i]
let name = coll.name
console.log('checkCollegeExist => College Name:: '+ name)
console.log('checkCollegeExist => Parameter => College Name:: '+collegeName)
if(String(name).valueOf() === String(collegeName).valueOf()){
responseToUser = 'Yes! CSUF has '+collegeName;
text = 'Yes! CSUF has '+collegeName;
}else{
responseToUser = 'CSUF does not teach ' +collegeName+' currently';
text = 'CSUF does not teach ' +collegeName+' currently';
}
}
}
else{
responseToUser = 'No more colleges';
}
if (requestSource === googleAssistantRequest) {
sendGoogleResponse(responseToUser);
} else {
sendResponse(text);
}
}

Answer 1

This is the culprit:
getCollegeData().then(buildSingleCollegeResponse(collegeName))
That calls buildSingleCollegeResponse(collegeName) and then passes its return value into then, just like foo(bar()) calls bar and passes its return value into foo.
You wanted to pass a functon to then:
getCollegeData().then(() => buildSingleCollegeResponse(collegeName))
// An arrow function ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Note that now that it's clear from the updated question that app.data.collegeData.college is an array, there's no need for Object.keys. Change:
let collegeLength = Object.keys(app.data.collegeData.college).length;
to simply
let collegeLength = app.data.collegeData.college.length;
Arrays have a length property (whereas non-array objects don't, by default).

Answer 2

You haven't mentioned what value app.data holds before issuing app.data.collegeData = data;
If app.data is undefined you should try app.data = {collegeData: data}
Or else negating what app stores. Following works
app = {};
app.data = {};
app.data.collegeData = data;
app.data.collegeData.college.length
You don't need to do the following
let collegeLength = Object.keys(app.data.collegeData.college).length;
Update: Refer to https://jsfiddle.net/dmxuum79/3/