DIV宽度更改时如何动态更改类？

Question

I know how to change classes with Jquery when the window size is changed, but I need it to be based on the width of a DIV and change dynamically when the DIV's width changes.

$(window).resize(function() {

   var wrapWidth = $('.info-wrap').width();

    if (wrapWidth >= 500) {

      $('#partOne').addClass('big');
      $('#partTwo').addClass('big');

    } else {

      $('#partOne').removeClass('big');
      $('#partTwo').removeClass('big');
    }
});

This works when the window size changes. But, what can I use insead of $(window).resize to get the width of the DIV as it changes?

Answer 1

Here is an example of observing the elements attributes.

See: MutationObserver and Mutation Events

CSS

#watch {
    border: 1px solid;
}

HTML

<button id="button">Click me</button>
<div id="watch" style="width: 100px; height: 50px;"></div>

Javascript

/*jslint sub: true, maxerr: 50, indent: 4, browser: true */
/* global global */

(function (global) {
    "use strict";

    if (typeof global.MutationObserver !== "function") {
        global.MutationObserver = global.WebKitMutationObserver || global.MozMutationObserver;
    }

    var watch = document.getElementById("watch");

    function whenClicked() {
        watch.style.width = "200px";
    }

    document.getElementById("button").addEventListener("click", whenClicked, false);

    if (typeof global.MutationObserver !== "function") {
        // chrome doesn't despatch an event for "DOMAttrModified"
        watch.addEventListener("DOMAttrModified", function (evt) {
            console.log("Attribute changed", evt.target);
        }, false);
    } else {
        var observer = new global.MutationObserver(function (mutations) {
            mutations.forEach(function (mutation) {
                if (mutation.type === 'attributes') {
                    console.log("Attribute changed", mutation);
                }
            });
        });

        observer.observe(watch, {
            attributes: true,
            childList: true,
            characterData: true,
            subtree: true
        });
    }
}(window));

On jsfiddle

Answer 2

I wrote a plugin sometime back for attrchange listener which basically adds a listener function on attribute change. This seems to come in handy for scenario that you had mentioned where you need a handler to check the width and height.

DEMO: http://jsfiddle.net/CKTk3/1/

    var prevWidth = $('#test').width(),
        prevHeight = $('#test').height();

    $('#test').attrchange({
        callback: function (e) {
            var curWidth = $(this).width(),
                curHeight = $(this).height();            
            if (prevWidth !== curWidth ||
                prevHeight !== curHeight) {
                console.log('resized: width - ' + prevWidth + ' : ' + curWidth + ' height - ' + prevHeight + ' : ' + curHeight);

                prevWidth = curWidth;
                prevHeight = curHeight;
            }            
        }
    }).resizable();

Plugin page: http://meetselva.github.io/attrchange/

Answer 3

I think you'll need to use a plugin for JQuery, such Ben Alman's plugin .

I don't think there exists something that detects when a div gets resize, only the window.

Answer 4

You can get div width by div class or id. ex: $("#div-id").width();