如何在JavaScript中释放键时进行测试

Question

I would like to have a variable become true when I press a key, and become false when it is released. I have a function that sets the var to true when the key is pressed, but I need to have a function called when a key is released as well to reset the var to false.

Answer 1

<input onkeydown="doX();" onkeyup="doY();" type="text">

<script type="text/javascript">     
   var flag = false;   
   function doX(){
      flag = true;        
   }

   function doY(){
     flag = false;    
   }
</script>

Expl:

There are two important keyboard events can help here.

1. keydown (will be fired when a key is pressed)
2. keyup (will be fired when a key is released)

call the doX function on keydown event and call doY function on keyup event!!

Code # 2:

<script type="text/javascript">
    var input = document.getElementById("test");
    var flag;       
    input.onkeydown = function(){
        flag = false;
    }

    input.onkeyup = function(){
        flag = true;
    }
</script> 

As, you asked to identify 'SPACE BAR', I have added the code here:

<script type="text/javascript">
    var input = document.getElementById("test");
    var flag;       
    input.onkeydown = function(e){
        var char = e.keyCode; //32 is for 'SPACE BAR'           
        flag = false;
    };

    input.onkeyup = function(e){
        var char = e.keyCode; //32 is for 'SPACE BAR'           
        flag = true;
    };
</script>