常用的高阶函数之控制执行次数

function limit(fn, limit, context) {
  let current = 0;
  return function(...args) {
    if (current >= limit) {
      return -1; // 或者返回其它有意义的内容
    }
    current += 1;
    
    let ctx = context || this;
    return fn.apply(ctx, args);
  }
}

function foo(id) {
  console.log(id);
}

foo(1); // log 1
foo(2); // log 2
foo(3); // log 3

foo = limit(foo, 1); // 限制只执行一次

foo(4); // log 4
foo(5); // do nothing
foo(6); // do nothing

function memorize(func, context) {
  let cache = {};
  return function(...args) {
    let address = args.length + args.join(",");
    if (cache[address] === undefined) {
    	cache[address] = func.apply(context || this, args);
    }
    return cache[address];
  };
};

// 使用斐波那契数列测试
let count = 0;
let fibonacci = n => {
  count ++;
  return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
}

for (let i = 0; i < 10; i ++) {
2fibonacci(i);
}
console.log(count); // 276

fibonacci = memorize(fibonacci);
count = 0;
for (let i = 0; i < 10; i ++) {
2fibonacci(i)
}
console.log(count); // 10