Load local JSON file into variable
JavascriptJqueryJsonJavascript Problem Overview
I'm trying to load a .json file into a variable in javascript, but I can't get it to work. It's probably just a minor error but I can't find it.
Everything works just fine when I use static data like this:
var json = {
id: "whatever",
name: "start",
children: [{
"id": "0.9685",
"name": " contents:queue"
}, {
"id": "0.79281",
"name": " contents:mqq_error"
}
}]
}
I put everything that's in the {}
in a content.json
file and tried to load that into a local JavaScript variable as explained here: <https://stackoverflow.com/questions/2177548/load-json-into-variable>;.
var json = (function() {
var json = null;
$.ajax({
'async': false,
'global': false,
'url': "/content.json",
'dataType': "json",
'success': function(data) {
json = data;
}
});
return json;
})();
I ran it with the Chrome debugger and it always tells me that the value of the variable json
is null
. The content.json
file resides in the same directory as the .js file that calls it.
What did I miss?
Javascript Solutions
Solution 1 - Javascript
My solution, as answered here, is to use:
var json = require('./data.json'); //with path
The file is loaded only once, further requests use cache.
edit To avoid caching, here's the helper function from this blogpost given in the comments, using the fs
module:
var readJson = (path, cb) => {
fs.readFile(require.resolve(path), (err, data) => {
if (err)
cb(err)
else
cb(null, JSON.parse(data))
})
}
Solution 2 - Javascript
For ES6/ES2015 you can import directly like:
// example.json
{
"name": "testing"
}
// ES6/ES2015
// app.js
import * as data from './example.json';
const {name} = data;
console.log(name); // output 'testing'
If you use Typescript, you may declare json module like:
// tying.d.ts
declare module "*.json" {
const value: any;
export default value;
}
Since Typescript 2.9+ you can add --resolveJsonModule compilerOptions in tsconfig.json
{
"compilerOptions": {
"target": "es5",
...
"resolveJsonModule": true,
...
},
...
}
Solution 3 - Javascript
If you pasted your object into content.json
directly, it is invalid JSON. JSON keys and values must be wrapped in double quotes ("
not '
) unless the value is numeric, boolean, null
, or composite (array or object). JSON cannot contain functions or undefined
values. Below is your object as valid JSON.
{
"id": "whatever",
"name": "start",
"children": [
{
"id": "0.9685",
"name": " contents:queue"
},
{
"id": "0.79281",
"name": " contents:mqq_error"
}
]
}
You also had an extra }
.
Solution 4 - Javascript
A solution without require or fs:
var json = []
fetch('./content.json').then(response => json = response.json())
Solution 5 - Javascript
The built-in node.js module fs will do it either asynchronously or synchronously depending on your needs.
You can load it using var fs = require('fs');
Asynchronous
fs.readFile('./content.json', (err, data) => {
if (err)
console.log(err);
else {
var json = JSON.parse(data);
//your code using json object
}
})
Synchronous
var json = JSON.parse(fs.readFileSync('./content.json').toString());
Solution 6 - Javascript
There are two possible problems:
- AJAX is asynchronous, so
json
will be undefined when you return from the outer function. When the file has been loaded, the callback function will setjson
to some value but at that time, nobody cares anymore.
I see that you tried to fix this with 'async': false
. To check whether this works, add this line to the code and check your browser's console:
console.log(['json', json]);
2. The path might be wrong. Use the same path that you used to load your script in the HTML document. So if your script is js/script.js
, use js/content.json
Some browsers can show you which URLs they tried to access and how that went (success/error codes, HTML headers, etc). Check your browser's development tools to see what happens.
Solution 7 - Javascript
For the given json format as in file ~/my-app/src/db/abc.json:
[ { "name":"Ankit", "id":1 }, { "name":"Aditi", "id":2 }, { "name":"Avani", "id":3 } ]
inorder to import to .js file like ~/my-app/src/app.js:
const json = require("./db/abc.json");
class Arena extends React.Component{
render(){
return(
json.map((user)=>
{
return(
<div>{user.name}</div>
)
}
)
}
);
}
}
export default Arena;
Output:
Ankit Aditi Avani
Solution 8 - Javascript
To export a specific value from output.json (containing json shared on question) file to a variable say VAR :
export VAR=$(jq -r '.children.id' output.json)