What is the JavaScript Equivalent of print_r in PHP?

What is the JavaScript Equivalent of PHP print_r() function? In other words, how you can "print" a javascript object in a way that's readable by humans?

Code

You could use JSON.stringify, as following:

The HTML part

Let's create two links for demo:

<p><a id="print_demo" href="javascript:void(0);">Print object</a></p>

<p><a id="pretty_print_demo" href="javascript:void(0);">Pretty Print object</a>	

The JAVASCRIPT part

Remark: I use jQuery to handle events, but you can use plain javascript (if you prefer).

<script type="text/javascript">

	$(function() {

		// create an object
		var person = new Object();
		person.firstname = "John";
		person.lastname = "Doe";
		person.age = "35";

		// plain print
		$("#print_demo").click(function() {
			alert(JSON.stringify(person));
		});

		// pretty print
		$("#pretty_print_demo").click(function() {
			alert(JSON.stringify(person, null, '    '));
		});

	});

</script>

DEMO

Using the above code:

Click to Print object

Click to Pretty Print object

About Internet Explorer

JSON will not work (by default) on Microsoft Internet Explorer ≤ 9. For a cross browser implementation, get json2.js from https://github.com/douglascrockford/JSON-js and use the following code:

<!--[if lt IE 10]>
<script type="text/javascript" src="json2.js"></script>
<![endif]-->

Another alternative is json3 from https://github.com/bestiejs/json3.

References

From JSON docs

• JSON in JavaScript

From Mozilla docs

• The JSON object
• JSON.stringify