function debounce(fn,delay = 500){
var t = null;return function(){if(t != nul){clearTimeout(t)};
setTimeout(fn,delay);}}
//时间间隔超过500才执行
function throttle(fn,delay = 500){
var lasttime = new Date().getTime();//throttle方法执行时候发生
return function(){
var now = new Date().getTime();//onscroll被触发的时候发生
if(now - lasttime > 500){
fn();
lasttime = now;//每次执行后将时间设置称当前;
}}}
window.onscroll = debounce(function(){
console.log('调用了1次');},500)