javascript - 我可以创建一个隐式转换为数字的 JavaScript 对象吗？

Question

我想创建一个具有多个公共(public)变量和方法的类，但在应用算术运算符时表现为数字。示例:

 
            a = new hyperNum(4)
            a.func(4)
            a.assign(2.0)
            alert(a + 1.0) `//3.0`

我知道我可以重载 Number 对象，但我认为所有数字都会有一定的开销。 当我尝试从 Number 继承时，出现错误:

function hyperNum () {}
hyperNum.prototype = new Number();
hyperNum.prototype.z = function(q){this.q = q;}
h = new hyperNum(2);
h+5
/* error:
TypeError: Number.prototype.valueOf is not generic
    at Number.valueOf (native)
    at Number.ADD (native)
    at [object Context]:1:2
    at Interface. (repl:96:19)
    at Interface.emit (events:31:17)
    at Interface._ttyWrite (readline:309:12)
    at Interface.write (readline:147:30)
    at Stream. (repl:79:9)
    at Stream.emit (events:31:17)
    at IOWatcher.callback (net:489:16)

*/

编辑:

 hyperNum.prototype.valueOf = function(){return this.q;}

成功了。

但是，使用不同的对象还是仅仅扩展 Number 对象更好？

Answer 1

您只需实现 valueOf 即可，无需扩展 Number 即可:

function Foo(val) {
  this.val = val;
}
Foo.prototype.valueOf = function() {
  return this.val;
};
Foo.prototype.toString = function() {
  return "Foo: " + this.val;
};

display("f = " + f);                      // "f = 42"
display("f + 1 = " + (f + 1));            // "f + 1 = 43"
display("f * 2 = " + (f * 2));            // "f * 2 = 84"
display("f as a string = " + String(f));  // "f as a string = Foo: 42"

Live example