First Class Functions

Functions can be passed as arguments.

function foo(v1,v2,callback){
    console.log(v1,v2);
    callback();
}

foo("one","two", function(){
    console.log("three");
});

////Output:
//one two
//three

Event Driven Environment

Javascript stays in memory waiting for events.

$(document).ready(function(){
    console.log("Hello");

    $('button').on('click', function(){
        console.log("World!");
    });
});

////Output:
//Hello
//World!
//World!
//World!
//...

Closures

Retains state and scope after code executes.

$(document).ready(function(){
    var foo = 1;

    $('button').on('click', function(){
        foo++;
        console.log(foo);
    });
});

////Output:
//2
//3
//...

Scope

Scope refers to what variables are available for access.

var a = 1;

function foo(){
    var b = 2;
    console.log(a,b);
}
console.log(a,b);

////Output:
//1 2
//>>Reference Error: b is undefined

var a = 1;

function foo(){
    var a = 1;
    a = 3;
    console.log(a);
}
console.log(a);

////Output:
//3
//1

var a = 1;

function foo(){
    b = 2;
    console.log(a, b);
}
console.log(a, b);

////Output:
//1 2
//1 2

Context

Context is what the value of         is on the running code.

this

function foo(){
    console.log(this === window);
}

window.foo();

////Output:
//true

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

obj.foo();

///Output:
//false true

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

obj.foo.call(window);
//obj.foo.call(window, 1, 2, .. , n);
//obj.foo.apply(window, [1, 2, .. , n]);

///Output:
//true false

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

var boundFunction = obj.foo.bind(window);
boundFunction();

///Output:
//true false