【前端面试题】这些js功能你一定要学会

// 监听全局失败事件
window.addEventListener(
    'error',
    e => {
        // 如果不是图片，则退出执行
        if (e.target.nodeName !== 'IMG') return
        /** 获取图片重新请求次数的属性 */
        let retry = Number(e.target.getAttribute('retry'))
        // 开启一个定时器,这里每400ms执行一次
        const timer = setTimeout(() => {
            // 如果重试次数大于2，则取消重试，设置图片错误占位图片
            if (retry > 2) {
                // 图片使用占位图片url
                e.target.src =
                    'data:image/png;base64,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'
                // 清除定时器
                clearTimeout(timer)
            } else {
                // 次数+1
                retry += 1
                // 设置重试属性
                e.target.setAttribute('retry', retry)
                // 重新获取图片
                e.target.src = e.target.src
            }
        }, 400)
    },
    true
)
复制代码

const queue = [fn1, fn2, ...]
async function start(){
    // 等待所有任务都完成
    await Promise.all(
        queue.map(async (callback)=>{
            await callback()
        })
    )
    // 去做其他的事情
    do_otherthing()
}
复制代码

const queue = [fn1, fn2, ...]
async function start() {
    if (queuq.length == 0) return
    await queue[0]()
    queue.shift()
    start()
}
//或者使用for循环解决
for(let i=0;i<queue.length;i++){
    await queue[i]()
}
复制代码

function sleep1() {
    return new Promise(r => {
        setTimeout(() => {
            console.log(1)
            r(0)
        }, 5000)
    })
}
function sleep2() {
    return new Promise(r => {
        setTimeout(() => {
            console.log(2)
            r(0)
        }, 5000)
    })
}
const queue = [sleep1, sleep2]
async function start1(){
    // 等待所有任务都完成
    await Promise.all(
        queue.map(async (callback)=>{
            await callback()
        })
    )
    // 去做其他的事情
    console.log("start1任务完成")
}
async function start2() {
    if (queue.length == 0) return console.log("start2任务完成")
    await queue[0]()
    queue.shift()
    start2()
}
start1()
start2()
复制代码

if(history.scrollRestoration){
    history.scrollRestoration = "manual"
}
复制代码

    // 获取到的数据
    const data = xxx
    // 创建a标签下载
    const a = document.createElement('a');
    // 存到二进制大对象中
    const blob = new Blob([data]);
    const url = URL.createObjectURL(blob);
    a.setAttribute('href', url);
    a.setAttribute('download', `测试.txt`);
    a.click();
    URL.revokeObjectURL(url);