SOURCE

// 利用setTimeout 实现setInterval
let timer = null
function interval(func, wait){
    let subInterval = function(){
        func.call(null)
        timer = setTimeout(subInterval,wait)
    }
    timer = setTimeout(subInterval,wait)
}

// 调用
interval(function() {}, 20)

// 清除定时器

if(timer){
    window.clearTimeout(timer)
    timer = null
}