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jQuery: mouseenter event and mouseleave event cause flickering problem

黄舟Original: 2017-06-28 10:11:033360browse

Hello everyone. Today I am making a jquery plug-in for image magnifier. It is similar to the magnifying glass for product pictures on JD.com.

I found that after I bound mouseenter and mouseleave to the image object, when the mouse moves on the image, mouseenter and mouseleave will be triggered at the same time, causing flickering. But I don't expect mouseenter and mouseleave to be called repeatedly, or even at the same time. How to solve it? I have tried several methods online but to no avail.

Thank you all.

$.fn.magnify = function() {
    //var glassBox = options.glassBox || {};
    //var detailBox = options.detailBox || {};

    var glassBox = $(&#39;<span></span>&#39;);

    glassBox.css({
        "width": this.width() / 2 + &#39;px&#39;,
        "height": this.height() /2 + &#39;px&#39;,
        "background-color": &#39;grey&#39;,
        "position": "absolute",
        "left" : &#39;0px&#39;,
        "top": &#39;0px&#39;,
        &#39;opacity&#39;: &#39;0.2&#39;,
        &#39;display&#39;: &#39;none&#39;,
        &#39;border&#39;: &#39;1px solid blue&#39;,
        &#39;z-index&#39;: 10

    });

    $(this).after(glassBox);
    //glassBox.hide();

    var detailBox = $(&#39;<div></div>&#39;);
    var detailImage = $(&#39;<img></img>&#39;);
    
    detailBox.css({
        "width": this.width(),
        "height": this.height(),
        "display": &#39;none&#39;,
        "position": &#39;relative&#39;,
        "overflow": &#39;hidden&#39;
        //"background-color": &#39;lime&#39;
    });
    detailImage.css({
        "position": &#39;absolute&#39;
    });
    detailImage.attr("src", this.attr("src"));
    detailBox.append(detailImage);
    this.after(detailBox);


    this.mouseenter(function(event){
        //event.stopPropagation();
        glassBox.get(0).style.display = &#39;block&#39;;
        detailBox.get(0).style.display = &#39;block&#39;;
        
        

    });
    this.mouseleave(function(event){    
        //event.stopPropagation();
        if (event.relatedTarget !== "span") {
            glassBox.get(0).style.display = &#39;none&#39;;
        detailBox.get(0).style.display = &#39;none&#39;;
        }
        
    });

    this.mousemove(function(event) {
        /* Act on the event */
        var x = event.pageX - this.offsetLeft - glassBox.width() / 2;
        var y = event.pageY - this.offsetTop - glassBox.height() /2;
        if (x < 0 ) {
            x = 0;
        } else if ( x > this.offsetWidth - glassBox.width()) {
            x = this.offsetWidth - glassBox.width();
        }
        if (y < 0) {
            y = 0;
        } else if (y > this.offsetHeight - glassBox.height()) {
            y = this.offsetHeight - glassBox.height();
        }
        glassBox.css({
            left: x + &#39;px&#39;,
            top:  y + &#39;px&#39;
        });

        detailImage.css({
        "left": -3.5 * (event.pageX - this.offsetLeft) + &#39;px&#39;,
        "top": -3.5 * (event.pageY - this.offsetTop) + &#39;px&#39;
    });
    });
}

HTML is as follows:

<html>
    <head>
        <script src="jquery-1.11.3.js"></script>
        <script src="magnify.js"></script>
    </head>
    <style>
        #imgTarget{
            width: 300px;
            height: 200px;
        }
        #imageArea{
            position: relative;
        }
    </style>
    <body>
        <div id="imageArea">
            <img id="imgTarget" src="car.jpg"/>
        </div>

        <script>
            $( document ).ready( function(){
                $("#imgTarget").magnify();
            } );

        </script>


    </body>


</html>

The reason for flickering is as follows:

You bound the mouseenter mouseleave event to img

when mouseenter img , you generated another glassBox

glassBox on the upper layer of img, thus blocking img and the mouse cursor, so a mouseleave

was generated for img, so the code set glassBox display=none again , the mouse can re-enter to img

Solution 1
Instead of using mouseenter mouseleave, directly judge whether the mouse position is within the range of img in mousemove.

Solution 2
Create an overlay with the same size as img:

<div id="imageArea">
 <img id="imgTarget" src="card.jpg"/>
 <div id="overlay"></div>
</div>

#overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 300px;
  height: 200px;
  background: red;
  opacity: 0.5;
  z-index: 3;
}

Ensure the z-index order of img glassBox overlay:

glassBox.css({
        "width": this.width() / 2 + &#39;px&#39;,
        "height": this.height() /2 + &#39;px&#39;,
        "background-color": &#39;grey&#39;,
        "position": "absolute",
        "left" : &#39;0px&#39;,
        "top": &#39;0px&#39;,
        &#39;opacity&#39;: &#39;0.2&#39;,
        &#39;display&#39;: &#39;none&#39;,
        &#39;border&#39;: &#39;1px solid blue&#39;,
        &#39;z-index&#39;: 2 // 保证glassBox在overlay的下面，在img的上面
    });

Events are bound On the overlay:

$( document ).ready( function(){
    $("#overlay").magnify(); 
} );

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