Looping over JSON array in JavaScript
last modified October 18, 2023
In this article we show how to loop over a JSON array in JavaScript.
The json-server is a JavaScript library to create testing REST API.
First, we create a project directory an install the json-server
module.
$ mkdir jsonforeach $ cd jsonforeach $ npm init -y $ npm i -g json-server
The JSON server module is installed globally with npm.
JSON test data
We have some JSON test data:
{
"users": [
{
"id": 1,
"first_name": "Robert",
"last_name": "Schwartz",
"email": "rob23@gmail.com"
},
{
"id": 2,
"first_name": "Lucy",
"last_name": "Ballmer",
"email": "lucyb56@gmail.com"
},
{
"id": 3,
"first_name": "Anna",
"last_name": "Smith",
"email": "annasmith23@gmail.com"
},
{
"id": 4,
"first_name": "Robert",
"last_name": "Brown",
"email": "bobbrown432@yahoo.com"
},
{
"id": 5,
"first_name": "Roger",
"last_name": "Bacon",
"email": "rogerbacon12@yahoo.com"
}
]
}
$ json-server --watch users.json
The --watch command is used to specify the data for the server.
$ curl localhost:3000/users/3/
{
"id": 3,
"first_name": "Anna",
"last_name": "Smith",
"email": "annasmith23@gmail.com"
}
With the curl command, we get the user with Id 3.
JSON forEach example
In the next example we retrieve data with a GET request using fetch API. We loop
over the returned data with forEach.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Home page</title>
</head>
<body>
<button id="log">Log</button>
<script src="main.js"></script>
</body>
</html>
This is the index.html page. By clicking on the Log
button, we fetch the data from the JSON server test data and log it into the
browser console.
const logBtn = document.getElementById('log');
logBtn.addEventListener('click', fetchData);
async function fetchData() {
const response = await fetch('http://localhost:3000/users/');
const data = await response.json();
data.forEach(obj => {
Object.entries(obj).forEach(([key, value]) => {
console.log(`${key} ${value}`);
});
console.log('-------------------');
});
}
The fetch function retrieves data as JSON array from the provided
URL. With forEach, we go through the array.
Object.entries(obj).forEach(([key, value]) => {
console.log(`${key} ${value}`);
});
We go over the entries of each object and print the key and the value to the console.
id 1 main.js:12:13 first_name Robert main.js:12:13 last_name Schwartz main.js:12:13 email rob23@gmail.com main.js:12:13 ------------------- main.js:14:9 id 2 main.js:12:13 first_name Lucy main.js:12:13 last_name Ballmer main.js:12:13 email lucyb56@gmail.com main.js:12:13 ------------------- main.js:14:9 ...
This is the output in the browser console.
Source
In this article we have shown how to iterate over a JSON array with forEach.