JavaScript

Question 1

What is JavaScript

Answer 1

Javascript is used by programmers across the world to create dynamic and interactive web content like applications and browsers.

Question 2

Semicolons ;

Answer 2

Semicolons separate JavaScript statements.
let a, b, c; // Declare 3 variables
a = 5; // Assign the value 5 to a
b = 6; // Assign the value 6 to b
c = a + b; // Assign the sum of a and b to c

Question 3

JavaScript Values

Answer 3

The JavaScript syntax defines two types of values:

Fixed values

Variable values

In a programming language, variables are used to store data values.

JavaScript uses the keywords var, let and const to declare variables.

An equal sign is used to assign values to variables.

Question 4

JavaScript and Camel Case

Answer 4

Hyphens are not allowed in JavaScript. They are reserved for subtractions. firstName, lastName, masterCard, interCity.

Question 5

JavaScript Comments

Answer 5

//

Question 6

4 Ways to Declare a JavaScript Variable

Answer 6

4 Ways to Declare a JavaScript Variable:
Using var
Using let
Using const
Using nothing

Question 7

When to Use JavaScript const?

Answer 7

If you want a general rule: always declare variables with const.

If you think the value of the variable can change, use let.

The two variables price1 and price2 are declared with the const keyword.

These are constant values and cannot be changed.

The variable total is declared with the let keyword.

Question 8

JavaScript Let

Answer 8

Variables defined with let cannot be Redeclared.
let x = "John Doe";

let x = 0;

// SyntaxError: ‘x’ has already been declared

Variables defined with let must be Declared before use.

Variables defined with let have Block Scope.

Question 9

Block Scope

Answer 9

Block Scope in JavaScript.

Variables declared inside a { } block cannot be accessed from outside the block:

{
  let x = 2;
}
// x can NOT be used here

Variables declared with the var keyword can NOT have block scope.

Variables declared inside a { } block can be accessed from outside the block.

Question 10

Block Scope and LET

Answer 10

Redeclaring a variable inside a block will not redeclare the variable outside the block:

let x = 10;
// Here x is 10

{
let x = 2;
// Here x is 2
}

// Here x is 10

Question 11

JavaScript Const

Answer 11

Variables defined with const cannot be Redeclared.

Variables defined with const cannot be Reassigned.

Variables defined with const have Block Scope.

JavaScript const variables must be assigned a value when they are declared:

Use const when you declare:

A new Array
A new Object
A new Function
A new RegExp

Question 12

Arrays with CONST

Answer 12

// You can create a constant array:
const cars = ["Saab", "Volvo", "BMW"];

// You can change an element:
cars[0] = "Toyota";

// You can add an element:
cars.push("Audi");

Question 13

Constant Objects

Answer 13

// You can create a const object:
const car = {type:"Fiat", model:"500", color:"white"};

// You can change a property:
car.color = "red";

// You can add a property:
car.owner = "Johnson";

Question 14

3 data types

Answer 14

let length = 16;                               // Number
let lastName = "Johnson";                      // String
let x = {firstName:"John", lastName:"Doe"};    // Object

Question 15

JavaScript Functions

Answer 15

A JavaScript function is a block of code designed to perform a particular task.

A JavaScript function is executed when “something” invokes it (calls it).

Question 16

Functions example

Answer 16

function myFunction(p1, p2) {
  return p1 * p2;   // The function returns the product of p1 and p2
}

function name(parameter1, parameter2, parameter3) {
  // code to be executed
}

Question 17

Function parameters, arguments

Answer 17

Function parameters are listed inside the parentheses () in the function definition.

Function arguments are the values received by the function when it is invoked.

Inside the function, the arguments (the parameters) behave as local variables.

Question 18

Function Invocation

Answer 18

When an event occurs (when a user clicks a button)
When it is invoked (called) from JavaScript code
Automatically (self invoked)