JavaScript

JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc. — you can bet that JavaScript is probably involved.

Data and Structure types

Number JavaScript has only one type of number. Unlike many other programming languages, JavaScript does not define different types of numbers, like integers, short, long, floating-point etc.

 1, 75, 1000000, 0.99, -13

String A string (or a text string) is a series of characters

"John Doe", "whatevs", "Banana", "x0Xl33tH4x3rX0x"

Boolean A Boolean has one of two values, true or false

true, false

undefined undefined is the value of a variable with no value. This variable will also be the type of undefined.

let x
x == undefined

Null the value of nothing. It is supposed to be something that doesn’t exist.

let x = null
x == null

Symbol Every symbol value returned from Symbol() is unique. A symbol value may be used as an identifier for object properties; this is the data type’s primary purpose, although other use-cases exist.

let myName = Symbol('Mark')
let yourName = Symbol('Mark')
yourName === myName // => false

Object Objects can be seen as a collection of properties. Property values can be values of any type, including other objects, which enables building complex data structures. Properties are identified using key values. A key value is either a String or a Symbol value.

{
    key value
} {
    myNumber 12,
    myName 'Mark'
}

Array Arrays are a collection of ‘elements’. each element can be of any data type (including arrays) and these elements are accessed by their ‘index’ or their position in the array. these indexes start at 0 and increase for each element in the array.

[2, 4, 6, 8]
['Mark', 'Jake', 'Mick', 'Harrison']

Variables

Variables are containers for storing data values. variables are given a named reference to a value. That way an unpredictable value can be accessed through a predetermined name.

Variable keywords

variable keywords are used to declare the value of a variable.

  • var declares a variable with global scope
  • let declares a variable with a local scope
  • const declares a variable with a local scope, however it’s value cannot be changed after declaration.

Operators

Operators are used to assign values, compare values, perform arithmetic operations, and more.

Arithmetic Operators

used to perform arithmetic between variables and/or values.

  • + Addition
  • - Subtraction
  • * Multiplication
  • ** Exponentiation
  • / Division
  • % Modulus (division remainder)
  • ++ Increment
  • – Decrement

Assignment Operators

used to assign values to variables

  • =
  • +=
  • -=
  • *=
  • /=
  • %=

Comparison Operators

these operators are used to determine a truthy or falsy value. these can be used in conjunction with other statements to run or not run certain lines of code under certain conditions.

  • == is equal
  • != is not equal
  • === strictly equals
  • > greater than
  • < less than
  • >= greater than or equal too
  • <= less than or equal too

Logical Operators

Logical operators are used to determine the logic between variables or values.

  • && and
  • || or
  • ! not

Functions

Functions are one of the fundamental building blocks in JavaScript. A function is a reusable set of statements to perform a task or calculate a value. Functions can be passed one or more values and can return a value at the end of their execution.

Function Parameters An input to the function when the function is declared or defined. Parameters are used as variables inside the functions body. When the function is called, these parameters will have the value of whatever is passed in as arguments

Function Return Functions return (pass back) values using the return keyword. return ends function execution and returns the specified value to the location where it was called.

Conditional Statements

Conditional Statements are used to perform different actions based on different conditions.

  • if is used to specity a block of code to executed, if a condition is ‘truthy’
  • elseis used to specify a block of code to executed, if the same condition of a proceeding if statement is ‘falsy’
  • else if is used to specify a new condition to test if the first condition is false
  • switch this is used to specify many alternative conditions and corresponding blocks of code to be executed

Loops

Loops are blocks of code used to do the same thing, over and over again. Often referred to as iteration. A loop will usually have one or more of the following elements

Initializer this is the starting point of the loop, and generally will count as each new iteration of the loop runs.

Condition A conditional statement used to determine whether the loop continues to run, or stops.

Final-expression this generally increments the initializer with each successive loop until the condition is no longer true.

Types of Loops

for loop

for (initializer; condition; final-expression) {
  // code to run
}

while loop

initializer
while (condition) {
    // code to run

    final - expression
}

do while

initializer
do {
    // code to run

    final - expression
} while (condition)

Loop Statements

break If you want to exit a loop before all the iterations have been completed, you can use the break statement. a break statement will immediately exit the loop and make the browser move on to any code that follows it.

continue The continue statement works in a similar manner to break, but instead of breaking out of the loop entirely, it skips to the next iteration of the loop.

Classes

Classes are a template for creating objects. They encapsulate data with code to work on that data.

Make up of a Class

Declaration One way to define a class is using a class declaration. To declare a class, you use the class keyword with the name of the class. A class expression is another way to define a class. Class expressions can be named or unnamed

Constructor The constructor method is a special method for creating and initializing an object created with a class. There can only be one special method with the name “constructor” in a class.

Methods methods are actions that can be performed on objects. Think of it like a function that exists on the class. To access this method we will first have to access the an object with the class this method exists.

This a keyword used to reference the instance of the object in which this exists.