>var arr = ["ab","cd","ef"]
>var show = function(value,index,ar){ print(value) }
>arr.forEach(show)
ab
cd
ef

//value為當前元素值，index為當前元素在數組中的索引，ar為數組本身
functionShowResults(value, index, ar) {
document.write("value:" + value);
document.write("index: " + index);
document.write("name: " + this.name);
document.write("
");
}
varletters = ['ab', 'cd', 'ef'];
varscope = { name: 'scope' };
// ShowResults為回調函數，scope為回調設置上下文環境，使回調函數的this指向scope變量，scope為可選參數
letters.forEach(ShowResults,scope);