5.7 Variable Declaration¶

Re-declaration¶

Task 1: Declare the variables a, b, and c with the keywords var, let, const, respectively. And assign them the values of 1, 2, and 3, respectively.

var a = 1;
let b = 2;
const c = 3;

console.log(a, b, c);

The result is: 1 2 3

Task 2: Refer to task 1; re-declare the variables a, and b.

var a = 1;
let b = 2;
const c = 3;

var a;
let b;

console.log(a, b);

The result is: Uncaught SyntaxError: Identifier 'b' has already been declared

Task 3: Refer to task 1; re-declare the variables a, and c.

var a = 1;
let b = 2;
const c = 3;

var a;
const c;

console.log(a, c);

The result is: Uncaught SyntaxError: Identifier 'c' has already been declared

Assignment¶

Task 4: Assign 10 to myVar1.

var myVar1;

myVar1 = 10;
console.log(myVar1);

The result is: 10

Task 5: Assign 20 to myVar2.

let myVar2;

myVar2 = 20;
console.log(myVar2);

The result is: 20

Task 6: Assign 30 to myVar3.

const myVar3;

myVar3 = 30;
console.log(myVar3);

The result is: Uncaught SyntaxError: Missing initializer in const declaration

Re-assignment¶

Task 7: Re-assign 100 to myVar1.

var myVar1 = 10;

myVar1 = 100;
console.log(myVar1);

The result is: 100

Task 8: Re-assign 200 to myVar2.

let myVar2 = 20;

myVar2 = 200;
console.log(myVar2);

The result is: 200

Task 9: Reassign 300 to myVar3.

const myVar3 = 30;

myVar3 = 300;
console.log(myVar3);

The result is: Uncaught TypeError: Assignment to constant variable.

Hoisting¶

Task 10: Access the variable myVar before its declaration.

console.log(myVar);

var myVar = "Hello";

The result is: undefined

Task 11: Access the variable myVar before its declaration.

console.log(myVar);

let myVar = "Hello";

The result is: Uncaught ReferenceError: Cannot access 'myVar' before initialization

Task 12: Access the variable myVar before its declaration.

console.log(myVar);

const myVar = "Hello";

The result is: Uncaught ReferenceError: Cannot access 'myVar' before initialization

Window¶

Task 13: Log the value of window.a in the console.

var a = 1;

console.log(window.a);

The result is: 1

Task 14: Log the value of window.a in the console.

let a = 1;

console.log(window.a);

The result is: undefined

Task 15: Log the value of window.a in the console.

const a = 1;

console.log(window.a);

The result is: undefined

Summary¶