$('input').each(function () {
    var req = $(this).attr('data-val-required');
    if (undefined != req) {
        var label = $('label[for="' + $(this).attr('id') + '"]');
        var text = label.text();
        if (text.length > 0) {
            label.append('<span style="color:red"> *</span>');
        }
    }
});

$("video ID/CLASS/TAG source:first").addClass("active");

var VAR = document.getElementById/Name/TagName("video ID/CLASS/TAG");

VAR.addEventListener('ended', function(e) {
 // get the active source and the next video source.
 // I set it so if there's no next, it loops to the first one
 var activesource = document.querySelector("video ID/CLASS/TAG source.active");
 var nextsource = document.querySelector("video ID/CLASS/TAG source.active + source") || document.querySelector("video ID/CLASS/TAG source:first-child");

 // deactivate current source, and activate next one
 activesource.className = "";
 nextsource.className = "active";

 // update the video source and play
 VAR.src = nextsource.src;
 VAR.play();

});

The Battery Status API, more often referred to as the Battery API, provides information about the system's battery charge level and lets you be notified by events that are sent when the battery level or charging status change. This can be used to adjust your app's resource usage to reduce battery drain when the battery is low, or to save changes before the battery runs out in order to prevent data loss.

navigator.getBattery().then((battery) => {
  function updateAllBatteryInfo() {
    updateChargeInfo();
    updateLevelInfo();
    updateChargingInfo();
    updateDischargingInfo();
  }
  updateAllBatteryInfo();


  battery.addEventListener("chargingchange", () => {
    updateChargeInfo();
  });
  function updateChargeInfo() {
    console.log(`Battery charging? ${battery.charging ? "Yes" : "No"}`);
  }


  battery.addEventListener("levelchange", () => {
    updateLevelInfo();
  });
  function updateLevelInfo() {
    console.log(`Battery level: ${battery.level * 100}%`);
  }


  battery.addEventListener("chargingtimechange", () => {
    updateChargingInfo();
  });
  function updateChargingInfo() {
    console.log(`Battery charging time: ${battery.chargingTime} seconds`);
  }


  battery.addEventListener("dischargingtimechange", () => {
    updateDischargingInfo();
  });
  function updateDischargingInfo() {
    console.log(`Battery discharging time: ${battery.dischargingTime} seconds`);
  }
});

IE Favorite

if (window.external) {
  window.external.AddFavorite(location.href, document.title);
}

Mozilla Firefox Bookmark

if (window.sidebar) {
  window.sidebar.addPanel(location.href, document.title, "");
}

Opera Hotlist

if (window.opera && window.print) {
  this.title = document.title;
  return true;
}

Math.log10(number)

string.length

let textArea = document.getElementById("inputOne");
textArea.addEventListener("keydown", function(e){
    if(e.key === "Enter"){
      validate(e);
    }
});

funtion validate(e){
    alert('Enter is pressed');
}

let docTitle = document.title;

window.addEventListener("blur", () => {
  document.title = "Come back :(";
})

window.addEventListener("focus", () => {
  document.title = docTitle;
})

var contents = {};
var duplicates = false;

$('table tbody tr').each(function () {
 var tdContent = $(this).children('input').val();
 if (contents[tdContent]) {
  duplicates = true;
  return false;
 }
 contents[tdContent] = true;
});

if (duplicates) {
 console.log('duplicate');
}

var arr = [];
var result = [];

var frequency = arr.reduce(function (seen, currentItem) {
 if (currentItem in seen) {
  seen[currentItem] = seen[currentItem] + 1;
 } else { seen[currentItem] = 1; }
  return seen;
 }, {});

for (var key in frequency) {
 if (frequency[key] > 1) {
  result.push(key.split(',').map(function (currentItem) {
   return currentItem;
  }));
 }
}

if([A, B, C].includes(A)){
 console.log('included');
}

!isNaN(parseFloat(arg)) && isFinite(arg)