Fabric.js animate onchange callback not working - fabricjs

Question

The documentation of Fabric.js on animation mentions this onChange callback:
onChange: canvas.renderAll.bind(canvas)
However, when I try to substitute this with a custom function, the animation does not show. See this example; the down animation does not show, only the up animation. What is wrong with this code?
var canvas = new fabric.Canvas('canvas');
fabric.Object.prototype.set({
hasControls: false,
selectable: false,
hoverCursor: 'default',
originX: 'center',
originY: 'center'
});
rect1 = new fabric.Rect({
left: 200,
top: 0,
width: 50,
height: 50,
fill: 'red',
opacity: 0
});
canvas.add(rect1);
var button01 = new fabric.Circle({
left: 20,
top: 20,
radius: 10,
fill: '#c0c0c0',
strokeWidth: 1,
stroke: '#808080',
hoverCursor: 'pointer'
});
canvas.add(button01);
button01.on('mousedown', function(options) {
animate_down()
});
var text1 = new fabric.Text("Animate", {
fontFamily: 'Arial',
fontSize: 12,
fill: 'black',
left: 58,
top: 20,
});
canvas.add(text1);
function animate_down() {
rect1.animate({
'top': 300,
'opacity': 1
}, {
onChange: function() {
canvas.renderAll.bind(canvas)
/* some other code */
},
onComplete: animate_up,
duration: 2000,
});
}
function animate_up() {
rect1.animate({
'top': 0,
'opacity': 0
}, {
onChange: canvas.renderAll.bind(canvas),
duration: 2000,
});
}
#canvas {
border:1px solid #000000;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.3.5/fabric.min.js"></script>
<canvas id="canvas" width="300" height="300"></canvas>

Answer 1

You need to call canvas.requestRenderAll(); inside your callback. As you are just binding canvas to canvas.renderAll, but never called. Docs
DEMO
var canvas = new fabric.Canvas('canvas');
fabric.Object.prototype.set({
hasControls: false,
selectable: false,
hoverCursor: 'default',
originX: 'center',
originY: 'center'
});
rect1 = new fabric.Rect({
left: 200,
top: 0,
width: 50,
height: 50,
fill: 'red',
opacity: 0
});
canvas.add(rect1);
var button01 = new fabric.Circle({
left: 20,
top: 20,
radius: 10,
fill: '#c0c0c0',
strokeWidth: 1,
stroke: '#808080',
hoverCursor: 'pointer'
});
canvas.add(button01);
button01.on('mousedown', function(options) {
animate_down()
});
var text1 = new fabric.Text("Animate", {
fontFamily: 'Arial',
fontSize: 12,
fill: 'black',
left: 58,
top: 20,
});
canvas.add(text1);
function animate_down() {
rect1.animate({
'top': 300,
'opacity': 1
}, {
onChange: function() {
canvas.requestRenderAll();
/* some other code */
},
onComplete: animate_up,
duration: 2000,
});
}
function animate_up() {
rect1.animate({
'top': 0,
'opacity': 0
}, {
onChange: canvas.requestRenderAll.bind(canvas),
duration: 2000,
});
}
#canvas {
border:1px solid #000000;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.3.5/fabric.min.js"></script>
<canvas id="canvas" width="300" height="300"></canvas>