title: How to catch mouse-up event outside of element?
body: <p>I have simple Javascript code, similar to this one:</p>
  
  <pre><code>var mouseIsDown = false;
  ...
  function canvasMouseDown(e) {
    ...
    mouseIsDown = true;
  }
  function canvasMouseUp(e) {
    mouseIsDown = false;
  }
  function canvasMouseMove(e) {
    if (mouseIsDown) {
      ...
    }
  }
  </code></pre>
  
  <p>with implemention my own user interface for tranformations (translations, scalings and rotations) with canvas.</p>
  
  <p>Such implementation within <code>canvasMouseMove()</code> function check <code>mouseIsDown</code> variable. All works fine if user does not release mouse button when the cursor/pointer is outside of the canvas element. If that happen, the variable <code>mouseIsDown</code> stays <code>true</code> and is not turned off by <code>canvasMouseUp</code> function.</p>
  
  <p>What is easy fix or solution in pure JavaScript <em>(no jQuery)</em> for this issue?</p>