Skip to main content

Functional Programming

· 2 min read
Lex
Lex
Front End Engineer @ Baoxiaohe

参考：

// 面向过程const a = 1;const b = 2;const c = a + b;
// OOPclass Sum(){  add(a, b) {    return a+b;  }}const instance = new Sum();instance.add(1,3)
// 函数式编程function add(a,b){  return a+b;}add(1,2)

函数不是指function，而是数学上的映射关系

y = f(x)

高阶函数#

函数作为参数和返回值

纯函数#

  • same input same output
  • 执行过程没有副作用

cache

let _ = require("lodash");
function add(a, b) {  console.log('begin')  return a + b;}const resolver = (...args) =>JSON.stringify(args);
// function memoize(func,resolver){//   let cache ={}//   return (...args) =>{//     const key = resolver(...args)//     if(cache[key]){//       return check[key]//     }else{//       return (check[key] = func(...args))//     }//   }// }
const memoizeAdd = .memoize(add,resolver);console.log(memoizeAdd(1,2))console.log(memoizeAdd(1,2))console.log(memoizeAdd(1,2))

test

Curry#

let _ = require("lodash");function add(a, b, c) {  console.log("begin");  return a + b + c;}
// function curry(func) {//   const argsLength = func.length;//   let curried = (...args) => {//     if (args.length < argsLength) {//       return (...rest) => curried(...args, ...rest);//     }//     return func(...args);//   };//   return curried;// }
let curriedAdd = _.curry(add);console.log(curriedAdd(1, 2, 3));console.log(curriedAdd(1)(2, 3));console.log(curriedAdd(1)(2)(3));

组合#

let _ = require("lodash");
let str = "a";function add1(str) {  return str + 1;}function add2(str) {  return str + 2;}function add3(str) {  return str + 3;}
function flow(...fns) {  if (fns.length === 1) return fns[0];  return fns.reduce(    (a, b) =>      (...args) =>        a(b(...args))  );}
// let r1 = add3(add2(add1(str)));let flowed = _.flow(add3, add2, add1);let r1 = flowed("a"); // a321

函子#

PointFree#

把数据处理的过程先定义成一种与参数无关的合成运算

const { compose } = require("lodash/fp");let money = 500;money -= 100;money -= 100;
// PointFreefunction buyHouse(money) {  return money - 100;}function buyCar(money) {  return money - 100;}
let fn = compose(buyCar, buyHouse);fn(500);