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Introduction to JavaScript (staging)
course content

Course Content

Introduction to JavaScript (staging)

Introduction to JavaScript (staging)

1. Introduction
Writing our first codeOutput Using Variables 1/2Output Using Variables 2/2
2. JavaScript syntax
JavaScript SyntaxJavaScript VariablesJavaScript OperatorsIdentifiers in JavaScriptNaming IdentifiersReserved keywords in JavaScriptNaming Convention in JavaScript. Case StylesVariables Naming ConventionBoolean Naming ConventionConstant Naming ConventionFunction & Classes Naming ConventionMultiline StringsMultiline Strings. ConcatenatingCommenting in JavaScriptCommenting in JavaScript. Multi-line Comments
3. Data Types and Variables
What are Variables?What are Data-types?JavaScript and Type ConversionVar 1/3Var 2/3Var 3/3Let 1/2Let 2/2Constant 1/3Constant 2/3Constant 3/3Number 1/3Number 2/3Number 3/3Boolean 1/4Boolean 2/4Boolean 3/4Boolean 4/4Strings 1/5Strings 2/5Strings 3/5Strings 4/5Strings 5/5BigInt 1/3BigInt 2/3BigInt 3/3Symbols 1/3Symbols 2/3Symbols 3/3NullUndefinedNull vs Undefined

bookLet 2/2

let Does Not Allow Redeclaration

Redeclaration means declaring a variable again. As discussed in the previous chapter, we can redeclare the variable again and again with var but we cannot do that with the let keyword.


              
123

            
var number = 5;
var number = 3;
console.log(number);
copy

But a variable declared with let does not allow redeclaration.


              
123

            
let number = 5;
let number = 3; 
console.log(number);
copy

Task

A variable named country with two values Pakistan and England has been given declared for you using the let keyword but this code won’t run because let doesn’t allow redeclaration. Your task is to make changes in the below code so that we England as the output. There are two possible ways to do get the desired result.

Note: Solution-2 is not much preferable.

let Does Not Allow Hoisting

As discussed in the previous chapter, let does not allow hoisting i.e. we cannot use a variable before the declaration. Variables declared with the var keyword can be accessed or used before the declaration, for example.


              
123

            
planet = 'earth';
console.log(planet);
var planet;
copy

But let does not allow hoisting.


              
123

            
planet = 'earth';
console.log(planet);
let planet;
copy

Summary:

  • let is the newer way to declare variables.
  • let has block scope.
  • let does not allow redeclaration.
  • let does not allow hoisting.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 3. Chapter 8
toggle bottom row

bookLet 2/2

let Does Not Allow Redeclaration

Redeclaration means declaring a variable again. As discussed in the previous chapter, we can redeclare the variable again and again with var but we cannot do that with the let keyword.


              
123

            
var number = 5;
var number = 3;
console.log(number);
copy

But a variable declared with let does not allow redeclaration.


              
123

            
let number = 5;
let number = 3; 
console.log(number);
copy

Task

A variable named country with two values Pakistan and England has been given declared for you using the let keyword but this code won’t run because let doesn’t allow redeclaration. Your task is to make changes in the below code so that we England as the output. There are two possible ways to do get the desired result.

Note: Solution-2 is not much preferable.

let Does Not Allow Hoisting

As discussed in the previous chapter, let does not allow hoisting i.e. we cannot use a variable before the declaration. Variables declared with the var keyword can be accessed or used before the declaration, for example.


              
123

            
planet = 'earth';
console.log(planet);
var planet;
copy

But let does not allow hoisting.


              
123

            
planet = 'earth';
console.log(planet);
let planet;
copy

Summary:

  • let is the newer way to declare variables.
  • let has block scope.
  • let does not allow redeclaration.
  • let does not allow hoisting.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 3. Chapter 8
toggle bottom row

bookLet 2/2

let Does Not Allow Redeclaration

Redeclaration means declaring a variable again. As discussed in the previous chapter, we can redeclare the variable again and again with var but we cannot do that with the let keyword.


              
123

            
var number = 5;
var number = 3;
console.log(number);
copy

But a variable declared with let does not allow redeclaration.


              
123

            
let number = 5;
let number = 3; 
console.log(number);
copy

Task

A variable named country with two values Pakistan and England has been given declared for you using the let keyword but this code won’t run because let doesn’t allow redeclaration. Your task is to make changes in the below code so that we England as the output. There are two possible ways to do get the desired result.

Note: Solution-2 is not much preferable.

let Does Not Allow Hoisting

As discussed in the previous chapter, let does not allow hoisting i.e. we cannot use a variable before the declaration. Variables declared with the var keyword can be accessed or used before the declaration, for example.


              
123

            
planet = 'earth';
console.log(planet);
var planet;
copy

But let does not allow hoisting.


              
123

            
planet = 'earth';
console.log(planet);
let planet;
copy

Summary:

  • let is the newer way to declare variables.
  • let has block scope.
  • let does not allow redeclaration.
  • let does not allow hoisting.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Everything was clear?

How can we improve it?

Thanks for your feedback!

let Does Not Allow Redeclaration

Redeclaration means declaring a variable again. As discussed in the previous chapter, we can redeclare the variable again and again with var but we cannot do that with the let keyword.


              
123

            
var number = 5;
var number = 3;
console.log(number);
copy

But a variable declared with let does not allow redeclaration.


              
123

            
let number = 5;
let number = 3; 
console.log(number);
copy

Task

A variable named country with two values Pakistan and England has been given declared for you using the let keyword but this code won’t run because let doesn’t allow redeclaration. Your task is to make changes in the below code so that we England as the output. There are two possible ways to do get the desired result.

Note: Solution-2 is not much preferable.

let Does Not Allow Hoisting

As discussed in the previous chapter, let does not allow hoisting i.e. we cannot use a variable before the declaration. Variables declared with the var keyword can be accessed or used before the declaration, for example.


              
123

            
planet = 'earth';
console.log(planet);
var planet;
copy

But let does not allow hoisting.


              
123

            
planet = 'earth';
console.log(planet);
let planet;
copy

Summary:

  • let is the newer way to declare variables.
  • let has block scope.
  • let does not allow redeclaration.
  • let does not allow hoisting.

Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
Section 3. Chapter 8
Switch to desktopSwitch to desktop for real-world practiceContinue from where you are using one of the options below
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