CSS Media Query and Javascript/jQuery don't match up

Question

In my CSS I have a media query like so:

@media (min-width: 800px) { /* styles */ }

And then in my jQuery, I'm targeting the window width and performing some actions.

Edit: as per the answers below, I have changed this function but my JS and CSS still didn't align. The problem was fixed by using the Modernizr function as specified in the accepted answer.

$(window).resize(function() {
    var viewportWidth = $(window).width();
    if (viewportWidth >= 800) {
        // do something
    }
});

The problem is that while the jQuery is executing bang on 800px or more, the CSS is kicking in at 740px.

Is there a known problem with these not aligning? Or could there be something on my page affecting the CSS and why it's 740px not 800px? Maybe there's something else I should be using instead of $(window) ?

Edit: I've tested in Safari and it works perfectly. In Chrome and Firefox, the jQuery functions run spot on to 800px and so does the CSS. But in Chrome, the CSS actually runs after 740px, even though the media query is 800px - how can I get these to align perfectly?

Answer 1

You can use Modernizr to execute the media query in JS (the mq() method will return a boolean):

$(window).resize(function() {
    if (Modernizr.mq('(min-width: 800px)')) {
        // do something
    }
});

Answer 2

Move your width check, or else the viewportWidth variable will always be the same thing:

$(window).resize(function() {
    var viewportWidth = $(this).width();
    if (viewportWidth >= 800) {
        // do something
    }
});

Answer 3

Valid code would be:

$(window).resize(function() {

    var viewportWidth = $(window).width();

    if (viewportWidth >= 800) {
        // do something
    }
});

Everytime window resizes the new value will be stored in viewportWidth variable. In your code viewportWidth gets the only value of the $(window).width() when the page was loaded.

Answer 4

What I just tried, and it seems to work, is to use the CSS media query to style an object, and then use javascript to test if the object has that style. Javascript is asking CSS what the answer is, rather than having two parts of the page determine it separately:

CSS:

@media (min-width: 800px) {  
    #viewType {width:3px;}
}

HTML :

<div id="viewType" style="display:none"></div>

JavaScript:

var answer = ($("#viewType").width()==3)

Answer 5

I agree with Steve answer. the jquery(window).width(); is does not match with the media queries and even doesn't provide accurate window width size. here is my answer taken from Steve and modified.

CSS :
        @media (max-width: 767px) {

           //define your class value, anything make sure it won't affect your layout styling
           .open {
            min-width: 1px !important;
           }
        } 

        .open {
              min-width: 2px;
        }

Js :

// when re-sizing the browser it will keep looking for the min-width size, if the media query is invoked the min-width size will be change.

$(window).on('resize orientation', function() {

    var media = $('.open').css('min-width');

    if( media == '1px') // means < 767px 
    {       
        // do your stuff
    }

});

That's it~ hope it help.