[Solved] This confuses in javascript [duplicate]

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The value of this changes depending upon how the function was invoked;

Collection.prototype.onOpen(); // `this` refers to `Collection.prototype`
// vs
var c = new Collection();
c.onOpen(); // `this` refers to `c`
// vs
var o = {};
Collection.prototype.onOpen.call(o); // `this` refers to `o`
// vs
var foo = Collection.prototype.onOpen;
foo(); // `this` could be `window` or undefined

Perhaps a some examples will aid you in your understanding of how this changes

// set up
var o = {};        // So we have an empty Object called `o`
function foo() {   // and a function called `foo` which lets
    return this;   // us see the value of `this` by returning
}                  // it
o.bar = foo;       // and set `bar` of `o` to be `foo`, too

// example 1
foo(); // `window` if in global scope (see example 4 for other scopes)
// example 2
o.bar(); // `o`
// example 3
foo.call(o);  // `o`, same as `o.bar.call(o);`
foo.apply(o); // `o`, same as `o.bar.apply(o);`

// example 4, complex
(function () {    // IIFE creates a new scope
    "use strict"; // and let's have it in in strict mode
    function baz() {
        return this;
    }
    return baz();
}()); // = `this` from `baz` = undefined

// example 5, inheritance
function Fizz() {
}
Fizz.prototype.buzz = foo;
var fizz = new Fizz();
fizz.buzz(); // `fizz`

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solved This confuses in javascript [duplicate]