'var that = this' vs. 'Function.call'

gistfile1.js

MyObjectThingy.prototype.someFunction = function () {
    var that = this;
    
    OtherObject.doSomethingWithACallback(123, function () {
        that.done();
    });
};

MyObjectThingy.prototype.someFunction = function () {
    OtherObject.doSomethingWithACallback(123, function () {
        that.done();
    }.call(this));
};