Question

Just starting out with canvas and javascript and can’t get my head around why the setTimeout in this snippet isn’t working. I initially thought it would trigger each frame since it’s contained within the loop. I have tried moving it around within the animate function as well to no avail.

$(document).ready(function(){
var canvas = $('#myCanvas');
var context = canvas.get(0).getContext('2d');   

var Shape = function(x1,y1,x2,y2){
    this.x1 = x1
    this.y1 = y1
    this.x2 = x2
    this.y2 = y2
}

var shapes = new Array();

shapes.push(new Shape(0,0,50,50));
shapes.push(new Shape(50,50,50,50));
shapes.push(new Shape(0,100,50,50));
shapes.push(new Shape(50,150,50,50));
shapes.push(new Shape(0,200,50,50));

function animate(){
    for (i=0;i<shapes.length;i++){
        context.clearRect(0,0,500,500);
        context.fillRect(shapes[i].x1,shapes[i].y1,shapes[i].x2,shapes[i].y2);
        setTimeout(animate, 500);
    };
};
animate();
});

Answer 1

Something wrong in your animate().

• Do not do setTimeout in a loop. That will freeze your browser.
• The codes in for loop draw the rectangle and erase it immediately. That’s why you cannot see your animation.

Consider changing your code like this.

  var i = 0;
  function animate(){
      context.clearRect(0,0,500,500);
      context.fillRect(shapes[i].x1,shapes[i].y1,shapes[i].x2,shapes[i].y2);
      i++;
      if (i == shapes.length) i = 0;
      setTimeout(animate, 500);
  };
  animate();