小编Zen*_*eno的帖子

 var canvas = window.__canvas = new fabric.Canvas('c');
 canvas.backgroundColor = '#efefef';
 canvas.freeDrawingBrush.width = 10;
 canvas.renderAll();

 document.getElementById('drawingMode').addEventListener('click', function(e) {
   e.target.innerHTML = canvas.isDrawingMode ? 'Start freedrawing' : 'End freedrawing';
   canvas.isDrawingMode = !canvas.isDrawingMode;
 });

canvas {
  border: 1px solid #ccc;
  padding: 20px;
}
/*.canvas-class {
    border-left: 20px solid black;
    padding: 20px;
}*/

<button id="drawingMode">Start freedrawing</button>
<div class="wrapper">
  <canvas id="c" class="canvas-class" width="400" height="300" style="border:1px solid #ccc;"></canvas>
</div>