我如何限制 keydown JavaScript 事件？

Question

This is the file http://www.frysa.us/Arctext/Size.html

I tried to limit the font size using an if statement:

<script>
$(function(){

 var KEY_UP = 38;
 var KEY_DOWN = 40;

 //Set listener for keydown
 $(document).keydown(function(e){
 $("anything").html("- keydown -");
   switch(e.which){
   case KEY_UP:
 var fontsize = parseInt($("#example4").css("font-size")) + 2;
 $("#example4").css("font-size", fontsize+"px");

if (("#example4").css("font-size")<20){
alert("it is less than 20")
//some sort of code to limit the font-size
}


 break;
case KEY_DOWN:
 var fontsize = parseInt($("#example4").css("font-size")) - 2;
 $("#example4").css("font-size", fontsize+"px");
 break;
   }
 });

});
</script>

Not much luck.. Can someone point me in the right direction

Answer 1

You just have to convert the CSS string to an integer. Try this using replace :

var fontSize = $("#example4").css("font-size");
var intFontSize = parseInt(fontSize.replace('px',''));
if (intFontSize<20){
    alert("it is less than 20")
    //some sort of code to limit the font-size
}

(also, note that you have a typo, this line is missing the $ ):

if (("#example4").css("font-size")<20){