var compose = function(f,g) {
  return function(x) {
    return f(g(x));
  };
};

var toUpperCase = function(x) {
return x.toUpperCase();
};
var exclaim = function(x) {
return x + "!";
};
 
var shout = compose(
exclaim,
toUpperCase
);
 
console.log(shout("hello world")); //HELLO WORLD!
 

function comp1(arr) {
   return function(val) {
     return arr.reduce(function(x, y) {
       return y(x(val));
     });
   };
}

function comp2(arr) {
   return function(val) {
      return arr.reduce(function(x, y) {
        return y(x);   
      },val);
   };
}

var funArr = [toUpperCase, exclaim];
 
console.log(comp1(funArr)); // function...
console.log(comp1(funArr)("hello")); // HELLO!
 
console.log(comp2(funArr)); // function...
console.log(comp2(funArr)("hello")); // HELLO!

链接: https://fly63.com/article/detial/2046