SOURCE

let createArray = (min, max) => {
    let r = []
    let i = min
    while (i <= max) {
        r.push(i)
        i++
    }
    return r
}
function start1() {
    console.time('第一种用时')
    let a = createArray(1, 50000)
    let b = createArray(25000, 100000)
    let common = []
    let aPoint = 0
    let bPoint = 0
    while (aPoint < a.length) {
        if (a[aPoint] === b[bPoint]) {
            common.push(a[aPoint])
            aPoint++
            bPoint++
        } else if (a[aPoint] < b[bPoint]) {
            aPoint++
        } else if (a[aPoint] > b[bPoint]) {
            bPoint++
        }
    }
    console.timeEnd('第一种用时')
}
function start2() {
    console.time('第二种用时')
    let c = createArray(1, 50000)
    let d = createArray(25000, 100000)
    let common2 = []
    c.forEach(item => {
        d.forEach(_item => {
            if (item === _item) {
                common2.push(item)
            }
        })
    })
    console.timeEnd('第二种用时')
}
let timer
let num = 0
function clock() {
    clearTimeout(timer)
    timer = setTimeout(() => {
        num++
        document.body.append(num)
        clock()
    }, 1000)

}
clock()

<button onclick="start1()">算法1</button>
<button onclick="start2()">算法2</button>