function print(content){
    // 输出到html函数，可忽略
    const div = document.createElement('div')
    div.innerHTML = content
    document.body.appendChild(div)
}

function log(action) {
    requestIdleCallback(function () {
        print(action + ': done!')
        // Do something like sending analytics...
    },{timeout: 1000})
}

function doSomething(action) {
    print(action + ': executing...')
    // Do something...
    log(action)
}

doSomething('operation #1')
doSomething('operation #2')
print('another operation')
doSomething('operation #3')