code: function (object, index, nonSplicing) {
        if (nonSplicing) {
          this._objects[index] = object;
        }
        else {
          this._objects.splice(index, 0, object);
        }
        this._initObject(object);
        this.renderOnAddition && this.renderAll();
        return this;
      }
docs: Inserts an object to canvas at specified index and renders canvas.
  An object should be an instance of (or inherit from) fabric.Object
  @method insertAt
  @param object {Object} Object to insert
  @param index {Number} index to insert object at
  @param nonSplicing {Boolean} when `true`, no splicing (shifting) of objects occurs
  @return {fabric.Canvas} instance