JavaScript之函数式编程

1. 纯函数：无副作用(不改变参数，不依赖环境，不进行请求，I/O操作)；如map, slice等；

2. 声明式代码

   javascript

   // 命令式
   const makes = [];
   for (let i = 0; i < cars.length; i++) {
     makes.push(cars[i].make);
   }
   // 声明式
   const makes = cars.map(function(car){ return car.make; });

3. 函数柯里化

   javascript

   // 普通写法
   const add = function(x, y) {
       return x + y;
   }
   // curry
   const addCurry = x => y => (x + y);
   const addTen = addCurry(10);
   const num = addTen(1);

4. 函数组合

   javascript

   const toUpperCase = x => x.toUpperCase();
   const exclaim = x => x + '!';
   // 普通
   const shout = x => exclaim(toUpperCase(x));
   console.log(shout('what happened!'));
   // 函数组合
   const compose = (...funcList) => x => funcList.reduce((pre, cur) => cur(pre), x);
   const shoutCompose = compose(toUpperCase, exclaim);
   console.log(shoutCompose('what happened!'));

5. Point Free：函数无须提及将要操作的数据是什么样的

   javascript

   // 非 pointfree，因为提到了数据：word
   const snakeCase = function (word) {
     return word.toLowerCase().replace(/\s+/ig, '_');
   };
   // pointfree
   const snakeCase = compose(replace(/\s+/ig, '_'), toLowerCase);