18 个高级工程师必须会的强大JavaScript 技巧

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()

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()

window.print()

print
noprint

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

const streamPromise = navigator.mediaDevices.getDisplayMedia()
streamPromise.then(stream => {
    var recordedChunks = [];// recorded video data
var 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);
    }
})

const streamPromise = navigator.mediaDevices.getDisplayMedia()
streamPromise.then(stream => {
    var recordedChunks = [];// recorded video data
var 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);
    }
})

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
);

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'])

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

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

  
Invisible
  
Invisible
  
Invisible

here can be edited

test
OK

console.dir(document.body)

phone
android message 
ios message
ios message