JSON Http Request

A common use of JSON is to read data from a web server, and display the data in a web page.

This chapter will teach you, in 4 easy steps, how to read JSON data, using XMLHttp.

JSON Example

This example reads a menu from myTutorials.txt, and displays the menu in a web page:

JSON Example

<div id="id01"></div>

<script>
var xmlhttp = new XMLHttpRequest();
var url = "myTutorials.txt";

xmlhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        var myArr = JSON.parse(this.responseText);
        myFunction(myArr);
    }
};
xmlhttp.open("GET", url, true);
xmlhttp.send();

function myFunction(arr) {
    var out = "";
    var i;
    for(i = 0; i < arr.length; i++) {
        out += '<a href="' + arr[i].url + '">' +
        arr[i].display + '</a><br>';
    }
    document.getElementById("id01").innerHTML = out;
}
</script>

Try it Yourself »

Example Explained

1: Create an array of objects.

Use an array literal to declare an array of objects.

Give each object two properties: display and url.

Name the array myArray:

myArray

var myArray = [
{
"display": "JavaScript Tutorial",
"url": "https://www.w3schools.com/js/default.asp"
},
{
"display": "HTML Tutorial",
"url": "https://www.w3schools.com/html/default.asp"
},
{
"display": "CSS Tutorial",
"url": "https://www.w3schools.com/css/default.asp"
}
]

2: Create a JavaScript function to display the array.

Create a function myFunction() that loops the array objects, and display the content as HTML links:

myFunction()

function myFunction(arr) {
    var out = "";
    var i;
    for(i = 0; i < arr.length; i++) {
        out += '<a href="' + arr[i].url + '">' + arr[i].display + '</a><br>';
    }
    document.getElementById("id01").innerHTML = out;
}

Call myFunction() with myArray as argument:

Example

myFunction(myArray);

Try it Yourself »

3: Create a text file

Put the array literal in a file named myTutorials.txt:

myTutorials.txt

[
{
"display": "JavaScript Tutorial",
"url": "https://www.w3schools.com/js/default.asp"
},
{
"display": "HTML Tutorial",
"url": "https://www.w3schools.com/html/default.asp"
},
{
"display": "CSS Tutorial",
"url": "https://www.w3schools.com/css/default.asp"
}
]

Look at the file »

4: Read the text file with an XMLHttpRequest

Write an XMLHttpRequest to read the text file, and use myFunction() to display the array:

XMLHttpRequest

var xmlhttp = new XMLHttpRequest();
var url = "myTutorials.txt";

xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
    var myArr = JSON.parse(this.responseText);
    myFunction(myArr);
    }
};

xmlhttp.open("GET", url, true);
xmlhttp.send();

Try it Yourself »

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