当你需要将当前屏幕显示为全屏时

function fullScreen() {      const el = document.documentElement    const rfs =     el.requestFullScreen ||     el.webkitRequestFullScreen ||     el.mozRequestFullScreen ||     el.msRequestFullscreen    if(typeof rfs != "undefined" && rfs) {        rfs.call(el)    }}fullScreen()

当你需要退出全屏时

function exitScreen() {    if (document.exitFullscreen) {         document.exitFullscreen()    }     else if (document.mozCancelFullScreen) {         document.mozCancelFullScreen()    }     else if (document.webkitCancelFullScreen) {         document.webkitCancelFullScreen()    }     else if (document.msExitFullscreen) {         document.msExitFullscreen()    }     if(typeof cfs != "undefined" && cfs) {        cfs.call(el)    }}exitScreen()

当您需要打印当前页面时

window.print()

当需要打印出当前页面，但又需要修改当前布局时

print
noprint

当需要阻止用户刷新或关闭浏览器时，可以选择触发beforeunload事件，部分浏览器无法自定义文本内容。

window.onbeforeunload = function(){    return "Are you sure you want to leave the haorooms blog？";};

当您需要录制当前屏幕并上传或下载屏幕录像时

const streamPromise = navigator.mediaDevices.getDisplayMedia()streamPromise.then(stream => {    var recordedChunks = [];// recorded video datavar options = { mimeType: "video/webm; codecs=vp9" };// Set the encoding format    var mediaRecorder = new MediaRecorder(stream, options);// Initialize the MediaRecorder instance    mediaRecorder.ondataavailable = handleDataAvailable;// Set the callback when data is available (end of screen recording)    mediaRecorder.start();    // Video Fragmentation    function handleDataAvailable(event) {        if (event.data.size > 0) {            recordedChunks.push(event.data);// Add data, event.data is a BLOB object            download();// Encapsulate into a BLOB object and download        }    }// file download    function download() {        var blob = new Blob(recordedChunks, {            type: "video/webm"        });        // Videos can be uploaded to the backend here        var url = URL.createObjectURL(blob);        var a = document.createElement("a");        document.body.appendChild(a);        a.style = "display: none";        a.href = url;        a.download = "test.webm";        a.click();        window.URL.revokeObjectURL(url);    }})

当你需要判断手机横屏或竖屏状态时

function hengshuping(){    if(window.orientation==180||window.orientation==0){        alert("Portrait state！")    }    if(window.orientation==90||window.orientation==-90){        alert("Landscape state！")    }}window.addEventListener("onorientationchange" in window ? "orientationchange" : "resize", hengshuping, false);

当你需要为横竖屏设置不同的样式时

当你需要监听标签显示和隐藏的事件时

const {hidden, visibilityChange} = (() => {    let hidden, visibilityChange;    if (typeof document.hidden !== "undefined") {      // Opera 12.10 and Firefox 18 and later support      hidden = "hidden";      visibilityChange = "visibilitychange";    } else if (typeof document.msHidden !== "undefined") {      hidden = "msHidden";      visibilityChange = "msvisibilitychange";    } else if (typeof document.webkitHidden !== "undefined") {      hidden = "webkitHidden";      visibilityChange = "webkitvisibilitychange";    }    return {      hidden,      visibilityChange    }})();const handleVisibilityChange = () => {    console.log("currently hidden", document[hidden]);};document.addEventListener(    visibilityChange,    handleVisibilityChange,    false);

当你从客户端获取图片但不能立即上传到服务器，需要预览时

        
<script>const getObjectURL = (file) => {    let url = null;    if (window.createObjectURL != undefined) { // basic        url = window.createObjectURL(file);    } else if (window.URL != undefined) { // webkit or chrome        url = window.URL.createObjectURL(file);    } else if (window.URL != undefined) { // mozilla(firefox)        url = window.URL.createObjectURL(file);    }    return url;}document.querySelector("input").addEventListener("change", (event) => {    document.querySelector("img").src = getObjectURL(event.target.files[0])})</script>

当你有很多图片时，你需要预加载图片以避免白屏

const images = []function preloader(args) {    for (let i = 0, len = args.length; i < len; i++) {          images[i] = new Image()          images[i].src = args[i]    } }  preloader(["1.png", "2.jpg"])

当需要将一串字符串转成js脚本时，该方法存在xss漏洞，慎用

const obj = eval("({ name: "jack" })")// obj will be converted to object{ name: "jack" }const v = eval("obj")// v will become the variable obj

当你需要写一个递归函数时，你声明了一个函数名，但是每次修改函数名时，你总是忘记修改内部函数名。argument是函数的内部对象，包括传入函数的所有参数，arguments.callee代表函数名。

// This is a basic Fibonacci sequencefunction fibonacci (n) {    const fn = arguments.callee    if (n <= 1) return 1    return fn(n - 1) + fn(n - 2)}

当需要判断一个dom元素当前是否出现在page view中时，可以尝试使用IntersectionObserver来判断。

  
Invisible
  
Invisible
  
Invisible
<script>  if (window?.IntersectionObserver) {    let items = [...document.getElementsByClassName("item")]; // parses as a true array, also available Array.prototype.slice.call()let io = new IntersectionObserver(      (entries) => {        entries.forEach((item) => {          item.target.innerHTML =            item.intersectionRatio === 1 // The display ratio of the element, when it is 1, it is completely visible, and when it is 0, it is completely invisible              ? `Element is fully visible`              : `Element is partially invisible`;        });      },      {        root: null,        rootMargin: "0px 0px",        threshold: 1, // The threshold is set to 1, and the callback function is triggered only when the ratio reaches 1      }    );    items.forEach((item) => io.observe(item));  }</script>

当你需要编辑一个dom元素时，让它像textarea一样点击

here can be edited

test
OK<script>  const el = document.getElementById("test");  let n = 1;  const observe = new MutationObserver((mutations) => {    console.log("attribute is changede", mutations);  })  observe.observe(el, {    attributes: true  });  function handleClick() {    el.setAttribute("style", "color: red");    el.setAttribute("data-name", n++);  }  setTimeout(() => {    observe.disconnect(); // stop watch  }, 5000);</script>

在开发过程中需要打印dom元素时，使用console.log往往只能打印出整个dom元素，无法查看dom元素的内部属性。您可以尝试使用 console.dir

console.dir(document.body)

当你在移动端开发时，你需要打开其他应用程序。location.href赋值也可以操作以下方法。

phoneandroid message ios messageios message

以上就是今天与你分享的18个JavaScript技巧。