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object-reference.js
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object-reference.js
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/**
* 对象的引用
*
* @参考资料:
* http://ejohn.org/apps/learn/#13
* http://ejohn.org/apps/learn/#14
* http://stackoverflow.com/questions/22216159/an-object-null-and-behaviour-in-javascript
*/
// Program 1
(function () {
var ninja = {
yell: function (n) {
return n > 0 ? ninja.yell(n - 1) + "a" : "hiy";
}
};
console.log(ninja.yell(4) == "hiyaaaa");
var samurai = {yell: ninja.yell};
var ninja = null;
try {
console.log(samurai.yell(4));
} catch (e) {
console.log(false, "Uh, this isn't good! Where'd ninja.yell go?");
}
// 这段代码无法正常工作,因为在 ninja.yell 方法内,又再次引用了 ninja 对象:
// return n > 0 ? ninja.yell(n-1) + "a" : "hiy";
// 因此,之后将 null 赋予给 ninja 后,这段代码就会抛出错误,因为 null 没有 yell 属性
})();
// Program 2
(function () {
var ninja = {
yell: function yell(n) { // 使用一个命名函数
return n > 0 ? yell(n - 1) + "a" : "hiy"; // 使用 yell 替代 ninja.yell
}
};
console.log(ninja.yell(4) == "hiyaaaa");
var samurai = {yell: ninja.yell}; // 在创建 ninja 对象之前 ninja.yell 就已经声明好了(是因为声明了一个命名函数 yell)
var ninja = null;
try {
console.log(samurai.yell(4));
} catch (e) {
console.log(false, "Uh, this isn't good! Where'd ninja.yell go?");
}
// Program 2 可以正常工作,因为创建了一个命名函数,然后将 ninja.yell 引用到了这个函数上
// Program 2 works because, instead of referring to the object that holds the function (ninja),
// you are giving the function a name and directly refer to that name.
})();