Class Ext.Element

var el = Ext.get("my-div");

// or with getEl
var el = getEl("my-div");

// or with a DOM element
var el = Ext.get(myDivElement);

Option    Default   Description
--------- --------  ---------------------------------------------
duration  .35       The duration of the animation in seconds
easing    easeOut   The YUI easing method
callback  none      A function to execute when the anim completes
scope     this      The scope (this) of the callback function

var el = Ext.get("my-div");

// no animation
el.setWidth(100);

// default animation
el.setWidth(100, true);

// animation with some options set
el.setWidth(100, {
    duration: 1,
    callback: this.foo,
    scope: this
});

// using the "anim" property to get the Anim object
var opt = {
    duration: 1,
    callback: this.foo,
    scope: this
};
el.setWidth(100, opt);
...
if(opt.anim.isAnimated()){
    opt.anim.stop();
}