Javascript是否有可能创建特定对象的原型Array？

Question

Helloworld,

I want to create a prototype of array.

Array.prototype.foo = function(){}

But my prototype must apply only if this array contain only a specific object like "bar" Is it possible to create a prototype like this in javascript? :

Array<bar>.prototype.foo = function(){}

Thank you! James

Answer 1

No, you can not.

You can check for the types in your current array.

 class Bar {} Array.prototype.foo = function() { if (this.some((n) => !(n instanceof Bar))) throw new Error('Incompatible type.'); console.log('called'); } let array = [1, 2]; try { array.foo(); } catch(e) { console.log(e.message); } array = [new Bar(), new Bar()]; array.foo(); 

Answer 2

One way to do this would be to check if your array contains bar before doing anything else, and stopping if it does not :

  Array.prototype.foo = function(){ if (this.indexOf('bar') === -1) { throw "The array must contain bar"; } // do what must be done console.log("all good"); } var rightOne = ['john', 'jane', 'bar']; var wrongOne = ['john', 'jane']; rightOne.foo(); wrongOne.foo(); 

Answer 3

I think that you can do something similar. The best way that I can think to do is it to decorate the default JavaScript array with an additional function. Below is an example showing a print function working.

 let test = ['a', 'b', 'c']; function decoratedArray(args) { let decorated = [...args]; decorated.print = () => { decorated.forEach((arg) => { console.log(arg); }); } return decorated; } test = decoratedArray(test); test.print(); 

Answer 4

With ES6 classes you could subclass an Array to get all it's internal methods, and add your own methods to it without modifying the native Array prototype.

 class Bar { constructor(id) { this.id = id } } class Foo extends Array { constructor(...args) { super(...args) } foo() { if (this.some(x => x instanceof Bar === false)) throw new Error('Foo can only contain Bar instances') console.log('All items are Bars') return this } } const pass = new Foo(new Bar(1), new Bar(2)) const fail = new Foo(new Bar(3), new Object) pass.foo() fail.foo()