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in Technique[技术] by (71.8m points)

for in 为什么不遍历对象原型上固有属性?

var triangle = { a: 1, b: 2, c: 3 };

Object.setPrototypeOf(triangle, { l: function add() {} });

function ColoredTriangle() {
  this.color = "red";
}

ColoredTriangle.prototype = triangle;

var obj = new ColoredTriangle();

for (var prop in obj) {
  console.log(`obj.${prop} = ${obj[prop]}`);
}

输出:
obj.color = red
obj.a = 1
obj.b = 2
obj.c = 3
obj.l = function add() {}

我们自定义的原型属性被打印了,但是对象的原型链上还有很多属性,为什么这些属性没被打印,难道是故意这么设计的?
image.png


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1 Answer

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by (71.8m points)

设计如此。

Iterating over own properties only.

for...in - JavaScript | MDN (mozilla.org)


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