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How to differentiate between let, const, and var in JavaScript / Observable
{
var number = 2;
number = 3; // This is "reassign"
var number = 4; // This is "redeclare"
return number
}
{
// VAR
var number = 2;
number = 3; // VAR can be reassigned
var number = 4; // VAR can be redeclared
return number
}
{
// LET
let number = 2;
number = 3; // LET can be reassigned
// let number = 4; // LET cannot be redeclared. TRY UNCOMMENTING THIS LINE
return number
}
{
// CONST
const number = 2;
// number = 3; // CONST cannot be reassigned. TRY UNCOMMENTING THIS LINE
// let number = 4; // CONST cannot be redeclared. TRY UNCOMMENTING THIS LINE
return number
}
{
const numbers = [1,2];
let newNumber = Math.floor(Math.random() * 10);
numbers.push(newNumber);
// numbers.pop(newNumber);
return numbers;
}
{
const ranking = {
Mike: 1,
Tom: 2,
Jack: 3
}
ranking.Tom = 20
return ranking.Tom
}
jsExample = {
// Global scope:
var global_one = "a global scoped variable declared by var";
let global_two = "a global scoped variable declared by let";
const global_three = "a global scoped variable declared by const";
if (4 > 3) {
// Block scope:
var block_one = "Block scoped variables created by var IS accessible outside the block"
let block_two = "Block scoped variables created by let is NOT accessible outside the block";
const block_three = "Block scoped variables created by const is NOT accessible outside the block";
}
// Function Scope:
function temperature(month) {
var normal_temp = 50;
let error = 10;
const constant = 0.5;
return normal_temp + error + constant + month
}
return global_one
// return block_two
// return block_one
// return temperature(12)
// return normal_temp
// return error
// return constant
}
{
var number = 1;
// let number = 1
if (true) {
var number = 3;
// let number = 3
}
return number
}
{
if (1 > 2) {
var impossible = 3;
// let impossible = 3;
}
impossible = 4;
return impossible
}
cellOne = 1
cellTwo = cellOne * 2
CellThree = {
let a = 0;
if (a < 1) {
a += 1; // LET can be reassigned.
}
return a
}
CellFour = CellThree * 3
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