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Explanation

* addEventListener
The addEventListener() method attaches an event handler to the specified element.
In context of a worker, both self and this refer to the global scope. The worker can either add an event listener for the message event, or it can define the onmessage handler to listen for any messages sent by the parent thread.
* postmessage
Pass a message to the worker.
* close()
Terminating Workers
Workers are resource-intensive; they are OS-level threads. Therefore, you do no want to create a large number of worker threads, and you should terminate the web worker after it completes its work. Workers can terminate themselves, like this:
self.close();
Reference: HTML DOM addEventListener() Method; The Basics of Web Workers

Explanation

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Explanation

Note:
* What is SVG?
SVG stands for Scalable Vector Graphics
SVG is used to define vector-based graphics for the Web
SVG defines the graphics in XML format
SVG graphics do NOT lose any quality if they are zoomed or resized
Every element and every attribute in SVG files can be animated
SVG is a W3C recommendation
* Example:
<script>
/* CONSTANTS */
var initialTheta = 0; // The initial rotation angle, in degrees.
var thetaDelta = 0.3; // The amount to rotate the square every "delay" milliseconds, in degrees.
var delay = 10; // The delay between animation stills, in milliseconds. Affects animation smoothness.
var angularLimit = 90; // The maximum number of degrees to rotate the square.
/*
Note that it will take the square (angularLimit/thetaDelta)*delay milliseconds to rotate an angularLimit number of degrees. For example, (90/0.3)*10 = 3000 ms (or 3 seconds) to rotate the square 90 degrees.
*/
/* GLOBALS */
var theSquare; // Will contain a reference to the square element, as well as other things.
var timer; // Contains the setInterval() object, used to stop the animation.
function init()
/*
Assumes that this function is called after the page loads.
*/
{
theSquare = document.getElementById("mySquare"); // Set this custom property after the page loads.
theSquare.currentTheta = initialTheta; // The initial rotation angle to use when the animation starts, stored in timer = setInterval(doAnim, delay); // Call the doAnim() function every "delay" milliseconds until "timer" is cleared.
}
function doAnim()
/*
This function is called by setInterval() every "delay" milliseconds.
*/
{
if (theSquare.currentTheta > angularLimit)
{
clearInterval(timer); // The square has rotated enough, instruct the browser to stop calling the doAnim() function.
return; // No point in continuing; stop now.
}
theSquare.setAttribute("transform", "rotate(" + theSquare.currentTheta + ")"); // Rotate the square by a small amount.
theSquare.currentTheta += thetaDelta; // Increase the angle that the square will be rotated to, by a small amount.
}
</script>
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