How to access the contents of a JSON file without a key? - json

Question

Basically, I am setting up a web server via Node.js and Express (I am a beginner at this) to retrieve data by reading a JSON file.
For example, this is my data.json file:
[{
"color": "black",
"category": "hue",
"type": "primary"
},
{
"color": "red",
"category": "hue",
"type": "primary"
}
]
I am trying to retrieve all of the colors by implementing this code for it to display on localhost:
router.get('/colors', function (req, res) {
fs.readFile(__dirname + '/data.json', 'utf8', function (err, data) {
data = JSON.parse(data);
res.json(data); //this displays all of the contents of data.json
})
});
router.get('/colors:name', function (req, res) {
fs.readFile(__dirname + '/data.json', 'utf8', function (err, data) {
data = JSON.parse(data);
for (var i = 0; i < data.length; i++) {
res.json(data[i][1]); //trying to display the values of color
}
})
});
How do I go about doing this?

Answer 1

What you are trying to do is actually pretty simple once you break it into smaller problems. Here is one way to break it down:
Load your JSON data into memory for use by your API.
Define an API route which extracts only the colours from your JSON data and sends them to the client as a JSON.
var data = [];
try {
data = JSON.parse(fs.readFileSync('/path/to/json'));
} catch (e) {
// Handle JSON parse error or file not exists error etc
data = [{
"color": "black",
"category": "hue",
"type": "primary"
},
{
"color": "red",
"category": "hue",
"type": "primary"
}
]
}
router.get('/colors', function (req, res, next) {
var colors = data.map(function (item) {
return item.color
}); // This will look look like: ["black","red"]
res.json(colors); // Send your array as a JSON array to the client calling this API
})
Some improvements in this method:
The file is read only once synchronously when the application is started and the data is cached in memory for future use.
Using Array.prototype.map Docs to extract an array of colors from the object.
Note:
You can structure the array of colors however you like and send it down as a JSON in that structure.
Examples:
var colors = data.map(function(item){return {color:item.color};}); // [{"color":"black"},{"color":"red"}]
var colors = {colors: data.map(function(item){return item.color;})} // { "colors" : ["black" ,"red"] }
Some gotchas in your code:
You are using res.json in a for loop which is incorrect as the response should only be sent once. Ideally, you would build the JS object in the structure you need by iterating over your data and send the completed object once with res.json (which I'm guessing internally JSON.stringifys the object and sends it as a response after setting the correct headers)
Reading files is an expensive operation. If you can afford to read it once and cache that data in memory, it would be efficient (Provided your data is not prohibitively large - in which case using files to store info might be inefficient to begin with)

Answer 2

in express, you can do in this way
router.get('/colors/:name', (req, res) => {
const key = req.params.name
const content = fs.readFileSync(__dirname + '/data.json', 'utf8')
const data = JSON.parse(content)
const values = data.reduce((values, value) => {
values.push(value[key])
return values
}, [])
// values => ['black', 'red']
res.send(values)
});
and then curl http://localhost/colors/color,
you can get ['black', 'red']

Answer 3

What you're looking to do is:
res.json(data[i]['color']);

Answer 4

If you don't really want to use the keys in the json you may want to use the Object.values function.
...
data = JSON.parse(data)
var values = []
for (var i = 0; i < data.length; i++) {
values.push(Object.values(data[i])[0]) // 0 - color, 1 - category, 2 - type
}
res.json(values) // ["black","red"]
...

Answer 5

You should never use fs.readFileSync in production. Any sync function will block the event loop until the execution is complete hence delaying everything afterwords (use with caution if deemed necessary). A few days back I had the worst experience myself and learnt that in a hard way.
In express you can define a route with param or query and use that to map the contents inside fs.readFile callback function.
/**
* get color by name
*
* #param {String} name name of the color
* #return {Array} array of the color data matching param
*/
router.get('/colors/:name', (req, res) => {
const color = req.params.name
const filename = __dirname + '/data.json';
fs.readFile('/etc/passwd', 'utf8', (err, data) => {
if(err){
return res.send([]); // handle any error returned by readFile function here
}
try{
data = JSON.parse(data); // parse the JSON string to array
let filtered = []; // initialise empty array
if(data.length > 0){ // we got an ARRAY of objects, right? make your check here for the array or else any map, filter, reduce, forEach function will break the app
filtered = data.filter((obj) => {
return obj.color === color; // return the object if the condition is true
});
}
return res.send(filtered); // send the response
}
catch(e){
return res.send([]); // handle any error returned from JSON.parse function here
}
});
});
To summarise, use fs.readFile asynchronous function so that the event loop is not clogged up. Inside the callback parse through the content and then return the response. return is really important or else you might end up getting Error: Can't set headers after they are sent
DISCLAIMER This code above is untested but should work. This is just to demonstrate the idea.

Answer 6

I think you can’t access JSON without key. You can use Foreach loop for(var name : object){} check about foreach it may help you