compose()主要是利用了数组的reduce()方法来实现迭代：第二个函数的执行结果，作为第一个函数的参数。
/**此处是源代码 * Composes single-argument functions from right to left. The rightmost * function can take multiple arguments as it provides the signature for * the resulting composite function. * * @param {...Function} funcs The functions to compose. * @returns {Function} A function obtained by composing the argument functions * from right to left. For example, compose(f, g, h) is identical to doing * (...args) => f(g(h(...args))). */ function compose(...funcs) { if (funcs.length === 0) { return arg => arg } if (funcs.length === 1) { return funcs[0] } return funcs.reduce((a, b) => (...args) => a(b(...args)))}复制代码 分析如下：
function compose(...funcs) { //reduce 数组元素的迭代,每次迭代都返回一个函数 //第二个函数的执行结果，作为第一个函数的参数 return funcs.reduce((a, b) => (...args) => a(b(...args)))}function f1(a){ return a+1;}function f2(a){ return a*10;}function f3(a){ return a-1;}var compo=compose(f1,f2,f3);console.log(compo);//Functionconsole.log(compo(3));//21复制代码 compose(f1,f2,f3)
//第一次迭代后的返回值(...args) => f1(f2(...args)) 等价于function fn(...args) { return f1(f2(...args));}复制代码 //第二次迭代后的返回值// return (...args) => fn(f3(...args)) 等价于// return (...args) => f1(f2(f3(...args))); 等价于// function fn(f3(...args)) {// return f1(f2(f3(...args)));// }复制代码 备注： 函数数组里面，最后一个函数可以有多个参数，其它函数只能有一个参数。