javascript - JS 的 for-in 和 in

Question

var result = function(){}
console.log("constructor" in result);//true
console.log("__proto__" in result);//true
console.log("prototype" in result);//true

for (var prop in result) {
   console.log(prop); // no output!!
}

当我使用 in 来确定结果中是否有属性时，它返回 true；但是当我使用for-in时，结果中没有属性，为什么？

Answer 1

引用:https://developer.mozilla.org/en/JavaScript/Reference/Statements/for...in

A for...in loop does not iterate over non–enumerable properties. Objects created from built–in constructors like Array and Object have inherited non–enumerable properties from Object.prototype and String.prototype that are not enumerable, such as String's indexOf method or Object's toString method. The loop will iterate over all enumerable properties of the object or that it inherits from its constructor's proptotype (including any which overwrite built-in properties).