14-4.txt

Javascript语言开发经典教程开发

<!-- The image that will be animated. Give it a name for convenience. -->
<IMG SRC="images/0.gif" NAME=animation>

<SCRIPT>
// Count how many images have been loaded. When we reach 10, start animating.
function count_images() {  if (++num_loaded_images == 10) animate(); }
var num_loaded_images = 0;

// Create the off-screen images and assign the image URLs.
// Also assign an event handler so we can count how many images have been
// loaded. Note that we assign the handler before the URL, because otherwise
// the image might finish loading (e.g., if it is already cached) before
// we assign the handler, and then we'll lose count of how many have loaded!
var images = new Array(10);
for(var i = 0; i < 10; i++) {
    images[i] = new Image();                 // Create an Image object.
    images[i].onload = count_images;         // Assign the event handler.
    images[i].src = "images/" + i + ".gif";  // Tell it what URL to load.
}

function animate()  // The function that does the animation.
{
    document.animation.src = images[frame].src;
    frame = (frame + 1)%10;
    timeout_id = setTimeout("animate()", 250);  // Display next frame later.
}
var frame = 0;         // Keep track of what frame of the animation we're on.
var timeout_id = null; // This allows us to stop the animation.
</SCRIPT>

<!-- Buttons to control the animation. Note that we don't let the user
  -- start the animation before all the images are loaded. -->
<FORM>                   
  <INPUT TYPE=button VALUE="Start" 
	 onClick="if (timeout_id==null && num_loaded_images==10) animate()">
  <INPUT TYPE=button VALUE="Stop" 
	 onClick="if (timeout_id) clearTimeout(timeout_id); timeout_id=null;">
</FORM>