节流、防抖

节流 ：在单位时间内，只触发一次。eg.scroll

function throttle(fn,delay=500){
	let flag = true
	return function(...args){
		let context = this
		if(!flag) return 
		flag = false
		setTimeout(()=>{
			fn.apply(context,args)
			flag = true
		},delay)
	}
}

防抖：事件触发n秒后再执行回调，n秒内触发，重新计时。eg.resize|change

function debounce(fn,delay=500){
	let timer = null
	return function(...args){
		let context = this
		timer && clearTimeout(timer)
		timer = setTimeout(()=>{
			fn.apply(context,args)
		},delay)
	}
}