<script type="text/javascript">//<![CDATA[
alert("I'm evaluated in the initial global execution context!");

setTimeout(function () {
    alert("I'm NOT evaluated in the initial global execution context.");
}, 1);
//]]></script>

function doWork(callbackfn, thisArg) {
    //...
    if (callbackfn != null) callbackfn.call(thisArg);
}

function MyType() {
    this.someData = "a string";
}

var instance = new MyType();
// Kind of like the following, but there are more steps involved:
// var instance = {};
// MyType.call(instance);

<script type="text/javascript">
if (true) {
    // Line A
}
</script>

<script type="text/javascript">
var obj = {
    someData: "a string"
};

function myFun() {
    // Line B
}

obj.staticFunction = myFun;

obj.staticFunction();
</script>

<script type="text/javascript">
var obj = {
    myMethod : function () {
        // Line C
    }
};
var myFun = obj.myMethod;
myFun();
</script>

<script type="text/javascript">
function myFun() {
    // Line D
}
var obj = {
    myMethod : function () {
        eval("myFun()");
    }
};
obj.myMethod();
</script>

<script type="text/javascript">
function myFun() {
    // Line E
}
var obj = {
    someData: "a string"
};
myFun.call(obj);
</script>

document.write(this);  //[object Window]

function f1()
{
   return this;
}
document.write(f1());  //[object Window]

function f()
{
    return this;
}

document.write(window.f()); //[object Window]

var obj = {
    name: "obj",
    f: function () {
        return this + ":" + this.name;
    }
};
document.write(obj.f());  //[object Object]:obj

var obj = {
    name: "obj1",
    nestedobj: {
        name:"nestedobj",
        f: function () {
            return this + ":" + this.name;
        }
    }
}

document.write(obj.nestedobj.f()); //[object Object]:nestedobj

var obj1 = {
    name: "obj1",
}

function returnName() {
    return this + ":" + this.name;
}

obj1.f = returnName; //add method to object
document.write(obj1.f()); //[object Object]:obj1

var context = "global";

var obj = {
    context: "object",
    method: function () {
        function f() {
            var context = "function";
            return this + ":" +this.context;
        };
        return f(); //invoked without context
    }
};

document.write(obj.method()); //[object Window]:global

/*********************************************************************
  1. When you add variable to the function using this keyword, it
     gets added to the function prototype, thus allowing all function
     instances to have their own copy of the variables added.
*********************************************************************/
function functionDef()
{
    this.name = "ObjDefinition";
    this.getName = function(){
        return this+":"+this.name;
    }
}

obj1 = new functionDef();
document.write(obj1.getName() + "<br />"); //[object Object]:ObjDefinition

/*********************************************************************
   2. Members explicitly added to the function protorype also behave
      as above: all function instances have their own copy of the
      variable added.
*********************************************************************/
functionDef.prototype.version = 1;
functionDef.prototype.getVersion = function(){
    return "v"+this.version; //see how this.version refers to the
                             //version variable added through
                             //prototype
}
document.write(obj1.getVersion() + "<br />"); //v1

/*********************************************************************
   3. Illustrating that the function variables added by both above
      ways have their own copies across function instances
*********************************************************************/
functionDef.prototype.incrementVersion = function(){
    this.version = this.version + 1;
}
var obj2 = new functionDef();
document.write(obj2.getVersion() + "<br />"); //v1

obj2.incrementVersion();      //incrementing version in obj2
                              //does not affect obj1 version

document.write(obj2.getVersion() + "<br />"); //v2
document.write(obj1.getVersion() + "<br />"); //v1

/*********************************************************************
   4. `this` keyword refers to the immediate parent object. If you
       nest the object through function prototype, then `this` inside
       object refers to the nested object not the function instance
*********************************************************************/
functionDef.prototype.nestedObj = { name: 'nestedObj',
                                    getName1 : function(){
                                        return this+":"+this.name;
                                    }
                                  };

document.write(obj2.nestedObj.getName1() + "<br />"); //[object Object]:nestedObj

/*********************************************************************
   5. If the method is on an object's prototype chain, `this` refers
      to the object the method was called on, as if the method was on
      the object.
*********************************************************************/
var ProtoObj = { fun: function () { return this.a } };
var obj3 = Object.create(ProtoObj); //creating an object setting ProtoObj
                                    //as its prototype
obj3.a = 999;                       //adding instance member to obj3
document.write(obj3.fun()+"<br />");//999
                                    //calling obj3.fun() makes
                                    //ProtoObj.fun() to access obj3.a as
                                    //if fun() is defined on obj3

var myname = "global context";
function SimpleFun()
{
    this.myname = "simple function";
}

var obj1 = new SimpleFun(); //adds myname to obj1
//1. `new` causes `this` inside the SimpleFun() to point to the
//   object being constructed thus adding any member
//   created inside SimipleFun() using this.membername to the
//   object being constructed
//2. And by default `new` makes function to return newly
//   constructed object if no explicit return value is specified

document.write(obj1.myname); //simple function

var ProtoObj = {
    fun: function () {
        return this.a;
    }
};
//Object.create() creates object with ProtoObj as its
//prototype and assigns it to obj3, thus making fun()
//to be the method on its prototype chain

var obj3 = Object.create(ProtoObj);
obj3.a = 999;
document.write(obj3.fun()); //999

//Notice that fun() is defined on obj3's prototype but
//`this.a` inside fun() retrieves obj3.a

function add(inc1, inc2)
{
    return this.a + inc1 + inc2;
}

var o = { a : 4 };
document.write(add.call(o, 5, 6)+"<br />"); //15
      //above add.call(o,5,6) sets `this` inside
      //add() to `o` and calls add() resulting:
      // this.a + inc1 + inc2 =
      // `o.a` i.e. 4 + 5 + 6 = 15
document.write(add.apply(o, [5, 6]) + "<br />"); //15
      // `o.a` i.e. 4 + 5 + 6 = 15

var g = add.bind(o, 5, 6);       //g: `o.a` i.e. 4 + 5 + 6
document.write(g()+"<br />");    //15

var h = add.bind(o, 5);          //h: `o.a` i.e. 4 + 5 + ?
document.write(h(6) + "<br />"); //15
      // 4 + 5 + 6 = 15
document.write(h() + "<br />");  //NaN
      //no parameter is passed to h()
      //thus inc2 inside add() is `undefined`
      //4 + 5 + undefined = NaN</code>

<script>
    function clickedMe() {
       alert(this + " : " + this.tagName + " : " + this.id);
    }
    document.getElementById("button1").addEventListener("click", clickedMe, false);
    document.getElementById("button2").onclick = clickedMe;
    document.getElementById("button5").attachEvent('onclick', clickedMe);
</script>

<h3>Using `this` "directly" inside event handler or event property</h3>
<button id="button1">click() "assigned" using addEventListner() </button><br />
<button id="button2">click() "assigned" using click() </button><br />
<button id="button3" onclick="alert(this+ ' : ' + this.tagName + ' : ' + this.id);">used `this` directly in click event property</button>

<h3>Using `this` "indirectly" inside event handler or event property</h3>
<button onclick="alert((function(){return this + ' : ' + this.tagName + ' : ' + this.id;})());">`this` used indirectly, inside function <br /> defined & called inside event property</button><br />

<button id="button4" onclick="clickedMe()">`this` used indirectly, inside function <br /> called inside event property</button> <br />

IE only: <button id="button5">click() "attached" using attachEvent() </button>

this

this

this

function foo() {
    console.log("bar");
    console.log(this);
}
foo(); // calling the function

var myObj = {key: "Obj"};
myObj.logThis = function () {
    // I am a method
    console.log(this);
}
myObj.logThis(); // myObj is logged

// continuing with the previous code snippet

var myVar = myObj.thisMethod;
myVar();
// logs either of window/global/undefined based on mode of operation

var el = document.getElementById('idOfEl');
el.addEventListener('click', function() { console.log(this) });
// the function called by addEventListener contains this as the reference to the element
// so clicking on our element would log that element itself

function Person (name) {
    this.name = name;
    this.sayHello = function () {
        console.log ("Hello", this);
    }
}

var awal = new Person("Awal");
awal.sayHello();
// In `awal.sayHello`, `this` contains the reference to the variable `awal`

function foo () { console.log (this, arguments); }
var thisArg = {myObj: "is cool"};
foo.call(thisArg, 1, 2, 3);

foo.apply(thisArg, [1,2,3])

function foo (a, b) {
    console.log (this, arguments);
}
var thisArg = {myObj: "even more cool now"};
var bound = foo.bind(thisArg, 1, 2);
console.log (typeof bound); // logs `function`
console.log (bound);
/* logs `function () { native code }` */

bound(); // calling the function returned by `.bind`
// logs `{myObj: "even more cool now"}, [1, 2]`

var myObj = {
    hello: function () {
        return "world"
        },
    myMethod: function () {
        // copy this, variable names are case-sensitive
        var that = this;
        // callbacks ftw o/
        foo.bar("args", function () {
            // I want to call `hello` here
            this.hello(); // error
            // but `this` references to `foo` damn!
            // oh wait we have a backup o/
            that.hello(); // "world"
        });
    }
  };

var person = {
    firstName: "Penelope",
    lastName: "Barrymore",
    fullName: function () {

    // We use "this" just as in the sentence above:
       console.log(this.firstName + " " + this.lastName);

    // We could have also written:
       console.log(person.firstName + " " + person.lastName);
    }
}

function foo() {
     // return an arrow function
     return (a) => {
     // `this` here is lexically inherited from `foo()`
     console.log(this.a);
  };
}
var obj1 = { a: 2 };
var obj2 = { a: 3 };

var bar = foo.call(obj1);
bar.call( obj2 ); // 2, not 3!

function someKindOfFunction() {
   this.style = 'foo';
}

<script type="text/javascript">
  console.log(this === window); // true
  var foo = "bar";
  console.log(this.foo); // "bar"
  console.log(window.foo); // "bar"

>this
  { ArrayBuffer: [Function: ArrayBuffer],
    Int8Array: { [Function: Int8Array] BYTES_PER_ELEMENT: 1 },
    Uint8Array: { [Function: Uint8Array] BYTES_PER_ELEMENT: 1 },
    ...
>global === this
 true

\test.js
console.log(this);  \ {}
console.log(this === global); \ fasle

<script type="text/javascript">
    foo = "bar";

    function testThis() {
      this.foo = "foo";
    }

    console.log(this.foo); //logs "bar"
    testThis();
    console.log(this.foo); //logs "foo"
</script>

<script type="text/javascript">
    foo = "bar";

    function testThis() {
      "use strict";
      this.foo = "foo";
    }

    console.log(this.foo); //logs "bar"
    testThis();  //Uncaught TypeError: Cannot set property 'foo' of undefined
</script>

<script type="text/javascript">
    foo = "bar";

    function testThis() {
      this.foo = "foo";
    }

    console.log(this.foo); //logs "bar"
    new testThis();
    console.log(this.foo); //logs "bar"

    console.log(new testThis().foo); //logs "foo"
</script>

function Thing() {
  console.log(this.foo);
}

Thing.prototype.foo = "bar";

var thing = new Thing(); //logs "bar"
console.log(thing.foo);  //logs "bar"

function Thing() {
    this.things = [];
}

var thing1 = new Thing();
var thing2 = new Thing();
thing1.things.push("foo");
console.log(thing1.things); //logs ["foo"]
console.log(thing2.things); //logs []

var obj = {
    foo: "bar",
    logFoo: function () {
        console.log(this.foo);
    }
};

obj.logFoo(); //logs "bar"

function Listener() {
    document.getElementById("foo").addEventListener("click",
       this.handleClick);
}
Listener.prototype.handleClick = function (event) {
    console.log(this); //logs "<div id="foo"></div>"
}

var listener = new Listener();
document.getElementById("foo").click();

function Listener() {
    document.getElementById("foo").addEventListener("click",
        this.handleClick.bind(this));
}
Listener.prototype.handleClick = function (event) {
    console.log(this); //logs Listener {handleClick: function}
}

var listener = new Listener();
document.getElementById("foo").click();

<div id="foo" onclick="console.log(this);"></div>
<script type="text/javascript">
document.getElementById("foo").click(); //logs <div id="foo"...
</script>

function Thing () {
}
Thing.prototype.foo = "bar";
Thing.prototype.logFoo = function () {
    eval("console.log(this.foo)"); //logs "bar"
}

var thing = new Thing();
thing.logFoo();

function Thing () {
}
Thing.prototype.foo = "bar";
Thing.prototype.logFoo = function () {
    with (this) {
        console.log(foo);
        foo = "foo";
    }
}

var thing = new Thing();
thing.logFoo(); // logs "bar"
console.log(thing.foo); // logs "foo"

<div class="foo bar1"></div>
<div class="foo bar2"></div>
<script type="text/javascript">
$(".foo").each(function () {
    console.log(this); //logs <div class="foo...
});
$(".foo").on("click", function () {
    console.log(this); //logs <div class="foo...
});
$(".foo").each(function () {
    this.click();
});
</script>

var val = "window.val"

var obj = {
    val: "obj.val",
    innerMethod: function () {
        var val = "obj.val.inner",
            func = function () {
                var self = this;
                return self.val;
            };

        return func;
    },
    outerMethod: function(){
        return this.val;
    }
};

//This actually gets executed inside window object
console.log(obj.innerMethod()()); //returns window.val

//Breakdown in to 2 lines explains this in detail
var _inn = obj.innerMethod();
console.log(_inn()); //returns window.val

console.log(obj.outerMethod()); //returns obj.val

var status = 1;
var helper = {
    status : 2,
    getStatus: function () {
        return this.status;
    }
};

var theStatus1 = helper.getStatus(); //line1
console.log(theStatus1); //2

var theStatus2 = helper.getStatus;
console.log(theStatus2()); //1

function Person(name){
    this.personName = name;
    this.sayHello = function(){
        return "Hello " + this.personName;
    }
}

var person1 = new Person('Scott');
console.log(person1.sayHello()); //Hello Scott

var person2 = new Person('Hugh');
var sayHelloP2 = person2.sayHello;
console.log(sayHelloP2()); //Hello undefined

function testFunc() {
    this.name = "Name";
    this.myCustomAttribute = "Custom Attribute";
    return this;
}

var whatIsThis = testFunc();
console.log(whatIsThis); //window

var whatIsThis2 = new testFunc();
console.log(whatIsThis2);  //testFunc() / object

console.log(window.myCustomAttribute); //Custom Attribute

<script type="application/javascript">
    function click_handler() {
        alert(this); // alerts the window object
    }
</script>

<button id='thebutton' onclick='click_handler()'>Click me!</button>

<script type="text/javascript" language="javascript">
$('#tbleName tbody tr').each(function{
var txt='';
txt += $(this).find("td").eq(0).text();
\same as above but synatx different
var txt1='';
 txt1+=$('#tbleName tbody tr').eq(0).text();
alert(txt1)
});
</script>

$('#a').click(function(){
console.log($(this).attr('href'));
});