详解JS中的compose函数和pipe函数用法

const calculate = x => (x + 10) * 10;
let res = calculate(10);
console.log(res);    // 200

const add = x => x + 10;
const multiply = x => x * 10;

// 我们的计算改为两个函数的嵌套计算，add函数的返回值作为multiply函数的参数
let res = multiply(add(10));
console.log(res);    // 结果还是200

// 参数从右往左执行，所以multiply在前，add在后
let res = compose(multiply, add)(10);

const arr = [[1, 2], [3, 4], [5, 6]];
// prevRes的初始值是传入的[]，以后会是每次迭代计算后的值
const flatArr = arr.reduce((prevRes, item) => prevRes.concat(item), []);

console.log(flatArr); // [1, 2, 3, 4, 5, 6]

const arr = [[1, 2], [3, 4], [5, 6]];
// prevRes的初始值是传入的[]，以后会是每次迭代计算后的值
const flatArr = arr.reduceRight((prevRes, item) => prevRes.concat(item), []);

console.log(flatArr); // [5, 6, 3, 4, 1, 2]

const compose = function(){
  // 将接收的参数存到一个数组， args == [multiply, add]
  const args = [].slice.apply(arguments);
  return function(x) {
    return args.reduceRight((res, cb) => cb(res), x);
  }
}

// 我们来验证下这个方法
let calculate = compose(multiply, add);
let res = calculate(10);
console.log(res);    // 结果还是200

const compose = (...args) => x => args.reduceRight((res, cb) => cb(res), x);

const pipe = function(){
  const args = [].slice.apply(arguments);
  return function(x) {
    return args.reduce((res, cb) => cb(res), x);
  }
}

// 参数顺序改为从左往右
let calculate = pipe(add, multiply);
let res = calculate(10);
console.log(res);    // 结果还是200

const pipe = (...args) => x => args.reduce((res, cb) => cb(res), x)