Skip to content

Latest commit

 

History

History
266 lines (181 loc) · 4.98 KB

README.md

File metadata and controls

266 lines (181 loc) · 4.98 KB

JavaScript 函数式编程手册 (ES6)

一份用 ES6 写的 JavaScript 函数式编程手册

Translations

概要

纯函数式

相同的参数返回相同的结果，它的执行不依赖于系统的状态

  1. 非纯净的
let number = 1;

const increment = () => number += 1;

increment();
// 2
  1. 纯净的
const increment = n => n + 1;

increment(1);
// 2

高阶函数

函数把其他函数当做参数传递使用或者返回一个函数

  1. 加法
const sum = (x, y) => x + y;

const calculate = (fn, x, y) => fn(x, y);

calculate(sum, 1, 2);
// 3
  1. filter
let students = [
    {name: 'Anna', grade: 6},
    {name: 'John', grade: 4},
    {name: 'Maria', grade: 9}
];

const isApproved = student => student.grade >= 6;

students.filter(isApproved);
// [ { name: 'Anna', grade: 6 }, { name: 'Maria', grade: 9 } ]
  1. Map
const byName = obj => obj.name;

students.map(byName);
// [ 'Anna', 'John', 'Maria' ]
  1. 链式
let students = [
    {name: 'Anna', grade: 6},
    {name: 'John', grade: 4},
    {name: 'Maria', grade: 9}
];

const isApproved = student => student.grade >= 6;

const byName = obj => obj.name;

students.filter(isApproved).map(byName);
// ['Anna', 'Maria']
  1. Reduce
const totalGrades = students.reduce((sum, student) => sum + student.grade, 0);

totalGrades
// 19

递归

当一个函数调用它自己的时候，就创造了一个循环

  1. 递减
const countdown = num => {
  console.log(num)
  num < 1
  ? num
  : countdown(num - 1)
}

countdown(5);
/*
5
4
3
2
1
0
*/
  1. 阶乘
const factorial = (num) =>
  num <= 0
  ? 1
  : n * factorial(num - 1)

factorial(5);
//120

Functor

有 map 方法的对象。functor 的 map 方法通过 map 回调函数调用自己的内容，然后返回一个新的 functor.

  1. 给数组所有的元素添加一个值
const plus1 = num => num + 1;

let numbers = [1, 2, 3];
numbers.map(plus1);
// [2, 3, 4]

组合

通过组合两个或更多的函数生成一个新的函数

  1. 组合两个函数生成一个新的函数
const compose = (f,g) => x => f(g(x));

const toUpperCase = x => x.toUpperCase();
const exclaim = x => `${x}!`;

const angry = compose(exclaim, toUpperCase);

angry("stop this");
// STOP THIS!
  1. 组合三个函数生成一个新的
const compose = (f,g) => x => f(g(x));

const toUpperCase = x => x.toUpperCase();
const exclaim = x => `${x}!`;
const moreExclaim = x => `${x}!!!!!`;

const reallyAngry = compose(exclaim, compose(toUpperCase, moreExclaim));

reallyAngry("stop this");
// STOP THIS!!!!!!

解构

从数组中提取数据或对象使用一种语法混合数组和对象文本的建设。或“模式匹配”。

  1. Select from pattern
const foo = () => [1, 2, 3];

const [a, b] = foo();
console.log(a, b);
// 1 2
  1. 接收 rest 值
const [a, ...b] = [1, 2, 3];
console.log(a, b);
// 1 [2, 3]
  1. 可选参数
const ajax = ({ url = "localhost", port: p = 80}, ...data)  =>
    console.log("Url:", url, "Port:", p, "Rest:", data);

ajax({ url: "someHost" }, "additional", "data", "hello");
// Url: someHost Port: 80 Rest: [ 'additional', 'data', 'hello' ]

ajax({ }, "additional", "data", "hello");
// Url: localhost Port: 80 Rest: [ 'additional', 'data', 'hello' ]

柯里化

一个函数有多个参数,把每个参数通过链式的形式返回下一个函数,直到最后返回结果。

  1. 对象柯里化
const student = name => grade => `Name: ${name} | Grade: ${grade}`;

student("Matt")(8);
// Name: Matt | Grade: 8
  1. 加法函数柯里化
const add = x => y => x + y;

const increment = add(1);
const addFive = add(5);

increment(3);
//4

addFive(10);
// 15

参考资源

https://gist.github.com/mikaelbr/9900818

https://www.gitbook.com/book/jcouyang/functional-javascript/details

https://www.youtube.com/playlist?list=PL0zVEGEvSaeEd9hlmCXrk5yUyqUag-n84

http://functionaljavascript.blogspot.com.br/2013/07/functors.html

http://nicoespeon.com/en/2015/01/pure-functions-javascript/

https://drboolean.gitbooks.io/mostly-adequate-guide/

https://www.youtube.com/watch?v=DisD9ftUyCk