JavaScript for C# developers

Dhananjay Kumar@debug_modeMicrosoft MVP

http://debugmode.net

Agenda Function as statement Function as expression Return statement Parameters in function The Arguments object Vargs JavaScript function Scopes in functions – global, local, and lexical this keyword JavaScript objects Object as literal Object using new operator or constructor pattern Object using static method Object.Create()

I am Dhananjay Kumar

6 times Microsoft MVP Developer Evangelist at

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We will learn everything by writing codes

JavaScript functionsFunction expression Function statement

A function expression creates an instance of the function object

It can be passed as an argument to a function

it can be returned from a function it can be assigned to a variable or an array Function created as an expression cannot

be executed before it is defined

It is must to give a name to function statement

For function statement, JavaScript creates an object and assigns that to a variable

Function created as statement are hoisted at the top, hence can be used before its defined

JavaScript functions : Return statement

A JavaScript function may or may not have a return statement

By default JavaScript function

returns undefined

JavaScript function can return a value or expression

If there is no expression with return statement, JavaScript function returns undefined In case of JavaScript constructor function, by default

function returns the invoking object instead of undefined

JavaScript functions : parameters

JavaScript does not do type checking of the parameters in function

JavaScript does not check the number of

parameters being passed to function

When less parameters are passed, non passed parameter would be undefined

When more parameters are passed, extra

parameters can be read using arguments object

JavaScript functions : arguments object

Along with parameters , arguments object also get passed to a JavaScript function. The arguments is an array like object, however it is not a pure array. Number of passed parameters can be find using arguments.length When more parameters are passed, extra parameters can be read in the arguments

objectValue of arguments object can be read using the indexes. JavaScript array push and pop operation cant be performed on arguments object

JavaScript functions :Varargs function

Varargs functions are those functions which work on any number of parametersUsing the arguments object, all the passed parameters can be iterated and used

JavaScript functions : scopes

temp can only be accessed inside function foo

temp is created using the function scope temp can’t be accessed outside function

foo

Scoping stands for the current context of code executionA variable or expression can be executed in the context of the function or in the global

context of JavaScript JavaScript does not have block scoping

JavaScript functions : scopes

Scopes

global

Functional/local

lexical

A variable which is not defined inside any function is in global scope.

Variable in the global scope can be used anywhere in the program

Variable inside a function works in local scope.

Variable in the local scope are accessible only inside the function

JavaScript functions : lexical scopeLexical scope works with the

nested functions.Lexical scoping means that

anything (function, object, variable) defined in the parent scope can be accessed inside the child scope. However the opposite is not true.

Let’s say there is a function “B” which is inside function “A”. The inner function B has access to the scope of the outer function A is lexical scoping

Function B is nested inside function A; The variable named myVar is created in the outer function A, so

can be accessed inside the child function B; The variable localVar is created inside the inner function B, so

cannot be accessed inside the outer function A;

JavaScript functions : this keyword“this” represents the calling

context in the global scope “this”

represents either a document or window object.

In the function scope (or inside the function), the value of “this” is determined by how the function is being called

In the strict mode, if we don’t set the calling base then the value of “this” would be set to undefined in the browsers.

Value of “this” is set to object calling the function

JavaScript objectsObjects can be created in three

possible ways.

Object as literal

Creating an object using the new operator and constructors

Creating an object using the Object.create() static method

Objects

Objects as literal

Object using function constructor or new operator

Object using Object.Create() static method

Q& A ?

Summary • Function as statement• Function as expression • Return statement• Parameters in function • The Arguments object• Vargs JavaScript function• Nested functions • Scopes in functions • this keyword• Function as constructor• Callback function • The call() and the apply() methods

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