javascript - 如何在 JavaScript 中向自定义类型添加方法

Question

如果标题措辞不当，请道歉。

我本质上要做的是创建一个具有方法的自定义类型。它旨在充当泛型类型，因此它可以接受 string、int 等

const foo = new CustomType('value')

console.log(foo) // 'value'
console.log(foo + 'hello') // 'valuehello'
foo.method() // Do something

const bar = new CustomType([])

bar.push('foobar')

如果我使用类来存储值，我无法对其进行操作。

class CustomType {
  constructor(value) {
    this.value = value
  }

  method() {}
}

const foo = new CustomType('value')
console.log(foo + 'hello') // [object Object]hello"

类似于如何使用new Array()或new String()

Answer 1

What you're trying to do is possible with prototypes (which is mimicked by classes in JS)

function CustomType(param) {
  this.default = param;
}

CustomType.prototype.toString = function(postfix = "") {
  return this.default + postfix;
};

CustomType.prototype.doSomething = function() {
  console.log("I am doing something")
};


let customTypedObject = new CustomType("value"); 
console.log(customTypedObject.toString());// "value
console.log(customTypedObject.toString("hello")); // "valuehello


//Prototypal function inherited
customTypedObject.doSomething() //"I am doing something"

Coercion Overriding

What you're actually explaining sounds a lot like overriding coercion rules in javascript which defines how a custom type behaves with another primitive type. This is also possible.

function CustomType(param) {
  this.default = param;
}
CustomType.prototype.valueOf = function() {
  return this.default;
}

let customTypedObject = new CustomType("value")
console.log(customTypedObject + "hello"); //valuehello

了解更多 here

If you are trying to override the browser's default approach to "toString()" an object. This is not possible. However there is a way to do this inside nodejs though. Node internally calls "inspect" on an object which is available in node js's root object prototype. This can be overriden

//Works on NodeJS code (not in browser)
CustomType.prototype.inspect = function() {
  return this.default;
};

let customTypedObject = new CustomType("value")
console.log(customTypedObject); // "value"