Array.prototype.slice.call(obj)
obj继承array的所有原形方法(prototype)；
obj有一下限制
Array.prototype.slice.call({name: 'obj'}) ; //[]
Array.prototype.slice.call({0: 'zero', 2: 'one', length: 2}); //["zero", empty]
Array.prototype.slice.call({name: 'zero', age: 'one', length: 2}); //[empty × 2]
Array.prototype.slice.call('sss'); //["s", "s", "s"]
Array.prototype.slice.apply('abc123!'); //["a", "b", "c", "1", "2", "3", "!"]
Array.prototype.slice.call({0: 'zero', 1: 'one', name: 'obj', length: 2}); //["zero", "one"]
