=== vs == , whats up?

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Javascript === vs == : Does it matter which “equal” operator I use?

In PHP and Javascript code i'm seeing more === out there as opposed to what I'm used to == for equality. Is === just a fancy way to write == ? Whats the deal with the xtra = sign?

PHP Code example:

<?php

// Parsing Yahoo! REST Web Service results using
// unserialize. PHP4/PHP5
// Author: Jason Levitt
// February 1, 2006

error_reporting(E_ALL);

// output=php means that the request will return serialized PHP
$request =  'http://yahoopipesURL';

$response = file_get_contents($request);

if ($response === false) {
 die('Request failed');
}

$phpobj = unserialize($response);

echo '<pre>';
print_r($phpobj);
echo '</pre>';

?>

Javascript Code example from one of my questions:

function setOrCreateMetaTag(metaName, name, value) {
    var t = 'meta['+metaName+'='+name+']';
    var mt = $(t);
    if (mt.length === 0) {
        t = '<meta '+metaName+'="'+name+'" />';
        mt = $(t).appendTo('head');
    }
    mt.attr('content', value);
}

setOrCreateMetaTag(name, viewport, 'width=device-width, initial-scale=1.0, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0');

Yep, thanks. It is a dupe. It's kind of funny that i couldn't find it in search because == and === is a site operator of some kind and doesn't work in the search box. — Chamilyan, Sep 20 '10 at 07:41
Don't feel bad, you *cannot* search for such characters. I found it on the FAQs, which are also very obscure - http://stackoverflow.com/tags/javascript/faq . Also, I've posted a link to JavaScript, but the idea is the same in PHP. — Kobi, Sep 20 '10 at 07:43
Thanks :). I've lived in the QA world for 10+ years so I'm always checking for dupes on auto pilot. This one slipped by me, but now I'll only feel a little bad. — Chamilyan, Sep 20 '10 at 08:02

score 3 · Answer 1 · answered Sep 20 '10 at 07:39

3

Since PHP and JavaScript are weakly typed, sometimes using == will cause unwanted coercions (e.g., convert a string to a number). The === operator is an identity operator—it only returns true if both operands are the same object.

answered Sep 20 '10 at 07:39

Mark Cidade

98,437
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score 2 · Answer 2 · answered Sep 20 '10 at 07:39

2

== is a value based comparison on javascript. Such as

x = 5
x == '5' //True

=== is a value and type based comparison so;

x = 5
x ==='5' //False, becaouse diffrent types

answered Sep 20 '10 at 07:39

Mp0int

18,172
15
83
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score 1 · Answer 3 · answered Sep 20 '10 at 07:45

'===' means exactly equal whereas '==' means equivalent within the current context.

This makes a big difference when comparing numbers as the following code snippet illustrates (stolen from the php docs):

<?php
$first = 10;
$second = 10.0;
$third = "10";

if ($first == 10) print "One";
if ($second == 10) print "Two";
if ($third == 10) print "Three";

if ($third === 10) print "Four";
if ($second === 10) print "Five";
if ($first === 10) print "Six";
?>
Will print out
OneTwoThreeSix

score 0 · Answer 4 · answered Sep 20 '10 at 07:51

in PHP, the extra = sign makes it absolute equality operator (===), which ensures/tests whether two values are the same and of the same data type, thus adding precision to comparisons. Here's a nice read from tuxradar: http://www.tuxradar.com/practicalphp/3/12/2

=== vs == , whats up?

4 Answers4