多态 是面向对象编程(OOP)的宗旨之一。它有助于设计对象，使其可以与特定提供的对象共享或覆盖任何行为。多态性 利用继承的 优势来实现这一点。
在以下示例中，子对象（例如“板球”和“网球”）已覆盖从父对象“游戏”调用的“选择”方法，并分别返回了新字符串，如输出所示。另一个子对象“足球”而不是覆盖select 方法，而是共享（继承）了该方法并显示了父字符串，如输出所示。
<html>
<body>
<script>
var game = function () {}
game.prototype.select = function() {
return " i love games and sports"
}
var cricket = function() {}
cricket.prototype = Object.create(game.prototype);
cricket.prototype.select = function() // overridden the select method to display { new string.
return "i love cricket"
}
var tennis = function() {}
tennis.prototype = Object.create(game.prototype); // overridden the select method to display new
tennis.prototype.select = function() string
{
return "i love tennis"
}
var football = function() {}
football.prototype = Object.create(game.prototype); // shared parent property
var games = [new game(), new cricket(), new tennis(), new football()];
games.forEach(function(game){
document.write(game.select());
document.write("</br>");
});
</script>
</body>
</html>i love games and sports i love cricket i love tennis i love games and sports