节流函数

// 声明thrttle函数
var throttle = function( fn, delay ){
    var timer = null;
    return function(){
        var context = this,
            args = arguments;

        clearTimeout(timer);
        timer = setTimeout(function(){
            fn.apply( context, args );
        }, delay);
    }
}

// 调用
throttle(function(){
    console.log('3秒后打印这个出来');
}, 3000);

function debounce(func, wait, immediate) {
    var timeout;
    return function() {
        var context = this, args = arguments;
        var later = function() {
            timeout = null;
            if (!immediate) func.apply(context, args);
        };
        var callNow = immediate && !timeout;
        clearTimeout(timeout);
        timeout = setTimeout(later, wait);
        if (callNow) func.apply(context, args);
    };
  }

// 添加resize的回调函数，但是只允许它每300毫秒执行一次
window.addEventListener('resize', debounce(function(event) {

    // 这里写resize过程

}, 300));