JS通过应用.css使元素移动

Question

I wanted to make an element move on arrow press by applying .css() but its not working at all and I cant figure out why. The exactly same code is working perfectly with JQ animate(). Can you explain me why the .css is not working ? I know there are better ways to do this but I'm just curious why its not attaching the top property.Below is the code with animate

$(document).ready(function(){
    $('body').keydown(function() {
        if (event.which == 38)
        {
            $('div').animate({top:'-=10px'},'fast');
        }
        else if (event.which == 40)
        {
            $('div').animate({top:'+=10px'},'fast');
        }
        else if (event.which == 37)
        {
            $('div').animate({left:'-=10px'},'fast');
        }
        else if (event.which == 39)
        {
            $('div').animate({left:'+=10px'},'fast');
        }
    }); 
});

Answer 1

Moving div require space to move or you can use position:absolute
Demo

Answer 2

Using .css() to adjust a property requires that property to be explicitly set beforehand, whereas .animate() will adjust the calculated position of an element without it being specifically set.

In the below snippet, I have given the #movable element top and left properties, and left the other <div> without them. The selector that .css() is applied to affects both <divs> , but note that only the <div> with the top and left properties moves.

 $(document).ready(function(){ $('body').keydown(function(event) { if (event.which == 38) { $('div').css({top:'-=10px'}); } else if (event.which == 40) { $('div').css({top:'+=10px'}); } else if (event.which == 37) { $('div').css({left:'-=10px'}); } else if (event.which == 39) { $('div').css({left:'+=10px'}); } //added to stop Stack Overflow scrolling event.preventDefault(); }); }); 

 div { position:relative; } /* Set top and left of the movable div explicitly */ #movable { top:0px; left:0px; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div id="movable">movable</div> <div>immovable</div> 

Answer 3

Is the code in the post your real code? Because you're using an event variable, but you haven't defined any argument to the function passed to keydown . It needs to be $('body').keydown(function(event) { .