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let timer; let
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flag
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/**
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* 节流原理：在一定时间内，只能触发一次
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*
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* @param {Function} func 要执行的回调函数
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* @param {Number} wait 延时的时间
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* @param {Boolean} immediate 是否立即执行
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* @return null
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*/
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function throttle(func, wait = 500, immediate = true) {
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if (immediate) {
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if (!flag) {
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flag = true
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// 如果是立即执行，则在wait毫秒内开始时执行
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typeof func === 'function' && func()
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timer = setTimeout(() => {
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flag = false
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}, wait)
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}
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} else if (!flag) {
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flag = true
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// 如果是非立即执行，则在wait毫秒内的结束处执行
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timer = setTimeout(() => {
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flag = false
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typeof func === 'function' && func()
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}, wait)
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}
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}
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export default throttle
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