1.写一个 mySetInterVal(fn, a, b),每次间隔 a,a+b,a+2b 的时间，然后写一个 myClear，停止上面的 mySetInterVal

function mySetInterval(fn, a, b){
    let timer = {id: null}
    function run(fn, a, b){
        timer.id = setTimeout(()=>{
            fn()
            console.log('间隔了' + a + 'ms')
            run(fn, a + b, b)
        },a)
    }
    run(fn , a, b)
    return timer
}
function myClear(timeId){
    clearTimeout(timeId)
}

// test
let timer = mySetInterval(() => {console.log('执行了fn函数')}, 200, 300)
setTimeout(()=>{
    myClear(timer.id)
}, 2000)