依赖注入:同一函数的rest和默认函数参数?

rest参数只能作为函数接受的最后一个参数使用,它捕获函数参数中未声明的所有参数。实际上,您可以放弃rest参数并传入一个数组

function a(numbers, _b = b) {
   return numbers.map(n => _b(n)); 
}

function b(n) {
   return n+1; 
}

console.log(a([1,2,3,4], f => f * 1));

Function.prototype.bind() (有点)解决了这个问题!

//The convention we will use here is that developers shouldn't use the 
// _underscore methods in production. 

export const _a = function(_b, ...numbers) {
 return numbers.map(n => _b(n)); 
}; 

export const b = function(n) {
  return n+1; 
}

export const a = _a.bind(null, b); 

console.log(a(1,2,3)) //[2,3,4]

现在你将如何测试这个?

import { _a } from "../functions";

describe("_a", () => {

    it("_a(1,2,3) calls _b three times.", () => {
        const mockFn = jest.fn();
        const a = _a.bind(null, mockFn);

        a(1, 2, 3);

        expect(mockFn.mock.calls).toHaveLength(3);
    })

}); 

如果你感兴趣的话-我已经开始 Github repo with a more fleshed out example of this approach here .