var n = 374; // allocates memory for a number
var s = "sessionstack"; // allocates memory for a string
var o = {
  a: 1,
  b: null,
}; // allocates memory for an object and its contained values
var a = [1, null, "str"]; // (like object) allocates memory for the
// array and its contained values
function f(a) {
  return a + 3;
} // allocates a function (which is a callable object)
// function expressions also allocate an object
someElement.addEventListener(
  "click",
  function () {
    someElement.style.backgroundColor = "blue";
  },
  false
);

var o1 = {
  o2: {
    x: 1,
  },
};
// 2 objects are created.
// 'o2' is referenced by 'o1' object as one of its properties.
// None can be garbage-collected

var o3 = o1; // the 'o3' variable is the second thing that
// has a reference to the object pointed by 'o1'.

o1 = 1; // now, the object that was originally in 'o1' has a
// single reference, embodied by the 'o3' variable

var o4 = o3.o2; // reference to 'o2' property of the object.
// This object has now 2 references: one as
// a property.
// The other as the 'o4' variable

o3 = "374"; // The object that was originally in 'o1' has now zero
// references to it.
// It can be garbage-collected.
// However, what was its 'o2' property is still
// referenced by the 'o4' variable, so it cannot be
// freed.

o4 = null; // what was the 'o2' property of the object originally in
// 'o1' has zero references to it.
// It can be garbage collected.

function f() {
  var o1 = {};
  var o2 = {};
  o1.p = o2; // o1 references o2
  o2.p = o1; // o2 references o1. This creates a cycle.
}

f();

function foo(arg) {
  bar = "some text";
}

// 等价于

function foo(arg) {
  window.bar = "some text";
}

function foo() {
  this.var1 = "potential accidental global";
}
// Foo called on its own, this points to the global object (window)
// rather than being undefined.
foo();

function scan(o) {
  Object.keys(o).forEach(function (key) {
    var val = o[key];

    // Stop if object was created in another window
    if (
      typeof val !== "string" &&
      typeof val !== "number" &&
      typeof val !== "boolean" &&
      !(val instanceof Object)
    ) {
      debugger;
      console.log(key);
    }

    // Traverse the nested object hierarchy
  });
}

var serverData = loadData();
setInterval(function () {
  var renderer = document.getElementById("renderer");
  if (renderer) {
    renderer.innerHTML = JSON.stringify(serverData);
  }
}, 5000); //This will be executed every ~5 seconds.

var theThing = null;
var replaceThing = function () {
  var originalThing = theThing;
  var unused = function () {
    if (originalThing)
      // a reference to 'originalThing'
      console.log("hi");
  };
  theThing = {
    longStr: new Array(1000000).join("*"),
    someMethod: function () {
      console.log("message");
    },
  };
};
setInterval(replaceThing, 1000);

function sayHi() {
  var allNames = [];
  return (name) => {
    allNames.push(name);
    return "👋 " + name;
  };
}

var hello = sayHi();

for (var i = 0; i < 1000000; i++) {
  hello("Gandhi");
}

var elements = {
  button: document.getElementById("button"),
  image: document.getElementById("image"),
};
function doStuff() {
  elements.image.src = "http://example.com/image_name.png";
}
function removeImage() {
  // The image is a direct child of the body element.
  document.body.removeChild(document.getElementById("image"));
  // At this point, we still have a reference to #button in the
  //global elements object. In other words, the button element is
  //still in memory and cannot be collected by the GC.
}

var element = document.getElementById("launch-button");
var counter = 0;
function onClick(event) {
  counter++;
  element.innerHtml = "text " + counter;
}
element.addEventListener("click", onClick);
// Do stuff
element.removeEventListener("click", onClick);
element.parentNode.removeChild(element);
// Now when element goes out of scope,
// both element and onClick will be collected even in old browsers // that don't handle cycles well.

// 子页面内
window.top.innerObject = someInsideObject
window.top.document.addEventLister(‘click’, function() { … });

// 外部页面
 innerObject = iframeEl.contentWindow.someInsideObject

<a href="#">Remove</a>
<iframe src="url" />

$('a').click(function(){
    $('iframe')[0].contentWindow.location.reload();
    // 线上环境实测重置 src 效果会更好
    // $('iframe')[0].src = "javascript:false";
    setTimeout(function(){
       $('iframe').remove();
    }, 1000);
});

window.onbeforeunload = function(){
    $(document).unbind().die();    //remove listeners on document
    $(document).find('*').unbind().die(); //remove listeners on all nodes
    //clean up cookies
    /remove items from localStorage
}

function send() {
  setInterval(function () {
    const data = {
      array1: get100Arrays(),
      array2: get500Arrays(),
    };

    let json = JSON.stringify(data);
    let arbfr = str2ab(json);
    worker.postMessage(arbfr, [arbfr]);
  }, 10);
}

function str2ab(str) {
  var buf = new ArrayBuffer(str.length * 2); // 2 bytes for each char
  var bufView = new Uint16Array(buf);
  for (var i = 0, strLen = str.length; i < strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  }
  return buf;
}

let ab = new ArrayBuffer(1);

try {
  worker.postMessage(ab, [ab]);

  if (ab.byteLength) {
    console.log("TRANSFERABLE OBJECTS are not supported in your browser!");
  } else {
    console.log("USING TRANSFERABLE OBJECTS");
  }
} catch (e) {
  console.log("TRANSFERABLE OBJECTS are not supported in your browser!");
}