Learn JavaScript

a series of statements together, a block of code, to perform a specific task.

The function asking to perform its task.

Pieces of information passed to a function.

The response of a function providing you an answer.

store blocks of code that you can later call at any time to avoid repetition in your program

Function Name

Creates a function that you can call later in your code.

A function with a name

A misplaced function where you would normally expect to see an expression. Ex. var area = function(width, height) {

A function with no name.

Functions not given a name. They are executed once the interpreter comes across them.

Parentheses to ensure the interpreter treats this as an expression.

function sayHello () {

function getArea(width, height) {

Calling functions that need information example

JavaScript treats _______ as first-class objects.

When something invokes and executes a function.

each word (except the first) begins with a capital letter

Tells the computer that you are making a function

Variable passed on. Values function will compute on

Where you write your block of reusable code.

Ends every line of code in a block of code.

Adds two values together or concatenates two strings into a single string.

Declares a variable.

Parameter is in

the reusable code that is between the curly brackets {}

To use the function, we _______ by just typing the function's name, and putting a parameter value inside parentheses after it. The computer will run the reusable code with the specific parameter value substituted into the code.

You want to use your code over and over again but you want to use that code with different inputs.

The computer can understand the code without spacing but it makes editing a lot easier and is best practice.

Put a _______at the end of each line of code in the reusable block and at the end of the entire function.

The semi-colon acts like a _______ in a sentence. It helps the computer know where there are stopping points in the code.

figuring out what went wrong with your code

Don't Repeat Yourself (D.R.Y) - The D.R.Y. principle

The part that you keep repeating will be this.

Gives the programmer back the value that comes out of the function.

keyword that gives the programmer back the value that comes out of the function

To call a function with more than one parameter.

Variables defined _______ a function are accessible anywhere once they have been declared.

Variables defined outside a function are _______ variables and their scope is _______.

who has more priority for the same name – glob vars or local vars?

defined inside a function; they cannot be accessed outside of that function

The var keyword creates a new variable in the _______ scope. That means if var is used outside a function, that variable has a global scope. If var is used inside a function, that variable has a local scope.

How many ways can js functions be evoked?

Each method differs in how this is initialized.

In JavaScript, the thing called this, is the object that "owns" the current code.

What is the value of "this" when used in a function?

Note that this is not a variable. It is a keyword. You cannot change the value of this.

The code in a function is not executed when the function is defined. It is executed when the function is invoked.

Some people use the term "call a function" instead of "invoke a function".It is also quite common to say "call upon a function", "start a function", or "execute a function".

In this tutorial, we will use invoke, because a JavaScript function can be invoked without being called.

with function expessions

Invoking a declared Function as a Function

The previous function does not belong to any object. But in JavaScript there is always a default global object.

In HTML the default global object is the HTML page itself, so the function above "belongs" to the HTML page.

In a browser the page object is the browser window. The function above automatically becomes a window function.

myFunction() and window.myFunction() is the same function:

This is a common way to invoke a JavaScript function, but not a good practice in computer programming.

When a function is called without an owner object, the value of this becomes the global object.

In a web browser the global object is the browser window.

Call the function

Invoking a function as a global function, causes the value of this to be the global object.

Using the window object as a variable can easily crash your program.

The fullName method is a function.

The function belongs to the object.

What is the owner of the fullName function?

The thing called this, is the object that "owns" the JavaScript code. In this case the value of this is myObject.

What is the difference between a user-defined object or a object constructor

What will be the value of "this" inside the code block of the function if we Invoke the function as the method of an object?

If a function invocation is preceded with the new keyword, it is a constructor invocation.

what is the difference between the function constructor and the object constructor?

A constructor invocation creates a new object. The new object inherits the properties and methods from its constructor.

it is like a class in php

The this keyword in the constructor does not have a value.

In JavaScript, functions are objects.

JavaScript functions have properties and methods.

What are the 2 predefined function methods by which we can invoke a function?

both methods must have the owner object as first parameter.

function myFunction(a, b) {

Where do we put the object when using apply() or call() methods?

The only difference is that call() takes the function arguments separately, and apply() takes the function arguments in an array.

In JavaScript strict mode, the first argument becomes the value of this in the invoked function, even if the argument is not an object. "so it creates an object from anying. "

With call() or apply() you can set the value of this inside the function and invoke the function as a new method of an existing object.

What do we make from a function with call and apply?

A JavaScript function does not perform any checking on parameter values (arguments).

Function parameters are the names listed in the function definition.

Function arguments are the real values passed to (and received by) the function.

If a function is called with missing arguments (less than declared), the missing values are set to: undefined

What is best solution when we call a function with less arguments

How to assign a default value to a parameter?

What does logical expressions do?

If y is defined, y || returns y, because y is true, otherwise it returns 0, because undefined is false.

if the variable is set or not.

If a function is called with too many arguments (more than declared), these arguments cannot be referred, because they don't have a name. They can only be reached in the arguments object.

JavaScript functions have a built-in object called the arguments object.

The argument array object contains an array of the arguments used in the function that was called (invoked).

it is equal to the alma element that it returns. its value is the alma element. the handler of the alma element.

nothing. x = getElementById("alma")