Javascript multiple matches for IF

Question

I'm trying to detect images in javascript, this is what I thought would work but it isn't. How can I do it correctly?

if (url.substr(url.length - 3 ) == 'gif' || 'jpg' || 'png')

What led you to believe that would work? – cookie monster Apr 21 '14 at 23:56 — cookie monster, Apr 21 '14 at 23:56

score 2 · Answer 1 · edited Apr 22 '14 at 00:10

2

You can't use the || in that fashion. You'd have to re-write the if statement as:

var lastThree = url.substr(url.length - 3);
if(lastThree == 'gif' ||
   lastThree == 'jpg' ||
   lastThree == 'png')
{
    // do something
}

Or you could use an array (which I would prefer personally):

if(['gif','jpg','png'].indexOf(url.substr(url.length - 3)) > -1)
{
    // do something
}

You should also use the toLowerCase() method on the URL substring, since some image files might end in JPG or GIF for example.

edited Apr 22 '14 at 00:10

numX

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answered Apr 21 '14 at 23:57

Justin Niessner

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EDIT: suggested use of toLowerCase method – numX Apr 22 '14 at 00:01

score 1 · Answer 2 · answered Apr 21 '14 at 23:56

1

You seem to misunderstand what an OR does:

var ext = url.substr(url.length - 3 );
if (ext == 'gif' || ext == 'jpg' || ext == 'png') {
   ..
}

answered Apr 21 '14 at 23:56

Christian Fritz

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RobG · Answer 3 · 2014-04-22T00:48:50.423

1

You can use a regular expression:

if (/gif|jpg|png/i.test(url.substr(url.length - 3 )))

Note that jpg can also be jpeg, gif might be giff and there is also tiff and other formats. And the extension is not reliable to determine a file format.

Edit

And as Cookie Monster suggests, you can save a bit of typing using:

/(gif|jpg|png)$/i.test(url)

and just add extras as required:

/(gif|jpg|jpeg|jfif|png|tiff|raw|bmp|svg)$/i.test(url)

edited Apr 22 '14 at 00:48

answered Apr 21 '14 at 23:59

RobG

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1

If you're going to use a regexp, why not just anchor it to the end of the string instead of using `substr`? – cookie monster Apr 22 '14 at 00:03

score 0 · Answer 4 · answered Apr 22 '14 at 00:00

0

You need to provide the complete condition after ||

    var src = url.substr(url.length - 3 );
    if (src === 'gif' || src === 'jpg' || src === 'png')

=== is used to check the value and type.

answered Apr 22 '14 at 00:00

Vinoth

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Javascript multiple matches for IF

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