High-Order Function.md

1. MEMORIZATION 记忆函数以牺牲空间复杂度的方法，利用闭包将需要重复计算的数据存储在闭包中，以便提高代码效率。减少不必要的重复计算

//递归模式记忆函数
var memorize = function(memo,formula){
    var recur = function(n){
        var result = memo[n];
        if(typeof result != "number"){
            memo[n] = formula(recur,n);
            result = memo[n];
        }
        return result;
        }
        return recur;
}
var fibonacci = memorize([0,1],function(recur,n){return recur(n-1)+recur(n-2)});

var factorial = memorize([1],function(recur,n){
    return n*recur(n-1)
});

2. Currying 柯里化函数本质目的是收集参数并且计算，其主要用途是提高代码模块化，还可以使函数延迟计算。

function curry(fn){
  var arr = arguments[1] || [];
  var len = fn.length;
  return function(){
    var innerArgs = Array.prototype.slice.call(arguments);
    return function(arg){
      if(arg.length === len){
        return fn.apply(null,arg);
      }
      else {
        return curry(fn,arg);
      }
    }(arr.concat(innerArgs))
  }
}

//通用叠加柯里化
function plus(num){
    var adder = function(){
        var args = [];
        var innerAdder = function(){
            args = args.concat([].slice.call(arguments));
            return innerAdder;5
        };
        innerAdder.toString = function(){
            return args.reduce(function(a,b){return a+b;})
        };
    }
    return adder()(num);
}

3. DEBOUNCE AND THROTTLE 函数去抖和函数节流两种方法是为了应用于类似mousemove此类事件触发太过频繁。 去抖的意思是防止重复调用，也就是说事件最后调用；节流的意思是防止调用次数太多，每隔interval事件调用一次

    function debounce(fn,delay){
        delay = delay || 200;
        var timer;
        return function(){
            var that = this;
            var arg = arguments;
            if(timer)
                clearTimeout(timer);
            timer = setTimeout(function(){
                timer = null;//释放内存好评！
                fn.apply(that,arg);
            },delay);
        };
    }

    function throttle(fn,interval = 200){
        var last;
        var timer;
        return function(){
            var that = this;
            var arg = arguments;
            var now = +new Date();
            if(last && now - last < interval){
                clearTimeout(timer);
                timer = setTimeout(function(){
                    last = now;
                    fn.apply(that,arg);
                },interval);
            }
            else {
                last = now;
                fn.apply(that,arg);
            }
        };
    }