nich nich - 1 month ago 5
Javascript Question

jquery: what does "$(this)" exactly mean?

I have a program and it works well.
See HERE.

This is the code:

<div id="round"></div>

<style>
#round{
position: absolute;
width: 200px;
height: 200px;
border-radius: 50%;
left: 400px;
top: 200px;
background-color: #e1e1e1;
}
</style>

<script src="jquery.js"></script>
<script src="jquery.easing.1.3.js"></script>
<script>
$(document).ready(function(){
$("#round").click(function(){
setInterval(function(){
$("#round").animate(
{height: 250,
width: 150,
top:150,
left: 425},
{duration: 300}
).
animate(
{height: 200,
width: 200,
top:200,
left: 400},
{duration: 300}
);
}, 0);
});
});
</script>


But when I change "#round" to "this". It won't work. why?
(actually it works, but when I put them into setInterval(), it won't work)

$(document).ready(function(){
$("#round").click(function(){
setInterval(function(){
$("#round").animate(
{height: 250,
width: 150,
top:150,
left: 425},
{duration: 300}
).
animate(
{height: 200,
width: 200,
top:200,
left: 400},
{duration: 300}
);
}, 0);
});
});


change to "this", it won't work.

$(document).ready(function(){
$("#round").click(function(){
setInterval(function(){
$(this).animate(
{height: 250,
width: 150,
top:150,
left: 425},
{duration: 300}
).
animate(
{height: 200,
width: 200,
top:200,
left: 400},
{duration: 300}
);
}, 0);
});
});

Answer

this is a reference to the member that invokes the current function...

then you can wrap it in the jquery function $() to select it just like you would another selector.

So setInterval calls a anonymous function so it is not invoked by a referencable member, so it defaults to the window object.

save the this context in a variable and then use it internally like this...

$(document).ready(function(){
    $("#round").click(function(){
        var clicked = this;   //<----store the click context outside setInterval
        setInterval(function(){
            $(clicked).animate(  //<----------use it here
                {height: 250,
                width: 150,
                top:150,
                left: 425},
                {duration: 300}
                ).
            animate(
                {height: 200,
                width: 200,
                top:200,
                left: 400},
                {duration: 300}
            );
        }, 0);
    });
});