typescript let vs const code example

Example 1: let vs const

`const` is a signal that the identifier won't be reassigned.

`let` is a signal that the variable may be reassigned, such as a counter in a
loop, or a value swap in an algorithm.

It also signals that the variable will be used only in the block it's defined
in, which is not always the entire containing function.

Example 2: var vs let vs const typescript

let num1:number = 1; 
    
function letDeclaration() { 
    let num2:number = 2; 

    if (num2 > num1) { 
        let num3: number = 3;
        num3++; 
    } 

    while(num1 < num2) { 
        let num4: number = 4;
        num1++;
    }

    console.log(num1); //OK
    console.log(num2); //OK 
    console.log(num3); //Compiler Error: Cannot find name 'num3'
    console.log(num4); //Compiler Error: Cannot find name 'num4'
}

letDeclaration();