使用原型的Javascript如何为数字设置“ this”的值？

Question

So if we can get past the "should you?" question ... does anyone know how to set the value of an integer in prototype?

 Number.prototype.add = function(num){ var newVal = this.valueOf() + num; this.valueOf(newVal); return newVal; } var rad = 4001.23; document.write(rad.add(10) + '<br/>' + rad); 

You'll notice rad.add(10) returns the number contained in the variable "rad" plus 10, but I would really like to change the value of rad from within the prototype add function (something I know this.valueOf(newVal) does not accomplish).

Can this be done? If so, how?

Answer 1

 Number.prototype.add = function(num){ var newVal = this.valueOf() + num; this.valueOf(newVal); return newVal; } var rad = new Number(4001.23); document.write(rad.add(10) + '<br/>' + rad); 

Answer 2

本质上你不能，数字，布尔值和字符串是不可变的

Answer 3

JavaScript has both number primitives and Number objects. Number primitives are immutable (like all primitives in JavaScript). The numeric value of a Number object is also immutable. So your add method can only return the updated value. You can create your own number-like object, of course, with a mutable value.

Details about number immutability and your own number object in this other answer (didn't realize that question was a duplicate when answering it) .