Var vs Let vs Const

varLetConst.js

// Hoisting
console.log(`var   before decleration : ${v}`);
console.log(`let   before decleration : ${l}`);
console.log(`const before decleration : ${c}`);


var v = 'VAR'
let l = 'LET'
const c = 'CONST'

// SCOPING
(() => {
	if (true) {
		var v = 'VAR';
		let l = 'LET';
		const c = 'CONST';

		console.log(`var   in block: ${typeof v !== 'undefined'? v:typeof v}`);
		console.log(`let   in block: ${typeof l !== 'undefined'? l:typeof l}`);
		console.log(`const in block: ${typeof c !== 'undefined'? c:typeof c}`);
	}
	try {
		console.log(`var   in function: ${typeof v !== 'undefined' ? v:typeof v}`);
		console.log(`let   in function: ${typeof l !== 'undefined' ? l:typeof l}`);
		console.log(`const in function: ${typeof c !== 'undefined' ? c:typeof c}`);
	} catch (e) {
		console.log(`${e.name} - ${e.message} in function scope`);
	}
})();
try {
	console.log(`var   out of function: ${typeof v !== 'undefined'? v:typeof v}`);
	console.log(`let   out of function: ${typeof l !== 'undefined'? l:typeof l}`);
	console.log(`const out of function: ${typeof c !== 'undefined'? c:typeof c}`);
} catch (e) {
	console.log(`${e.name} - ${e.message} out of function scope`);
}

// Redeclaration
(() => {
    if (true) {
        var v = 'VAR';
        let l = 'LET';
        const c = 'CONST';

        const v = 'VAR_re-declared';
        const l = 'LET_re-declared';
        const c = 'CONST_re-declared';

        try {
            console.log(`var   in function: ${typeof v !== 'undefined' ? v:typeof v}`);
            console.log(`let   in function: ${typeof l !== 'undefined' ? l:typeof l}`);
            console.log(`const in function: ${typeof c !== 'undefined' ? c:typeof c}`);
        } catch (e) {
            console.log(`${e.name} - ${e.message} in function scope`);
        }
    }
})();

// Reassignment
(() => {
    if (true) {
        var v = 'VAR';
        let l = 'LET';
        const c = 'CONST';

        try {

            v = 'VAR_UPDATED';
            l = 'LET_UPDATED';
            c = 'CONST_UPDATED'

        } catch (e) {
            console.log(`${e.name} - ${e.message}`);
        }
        console.log(`var   update: ${v}`);
        console.log(`let   update: ${l}`);
        console.log(`const update: ${c}`);
    }
    try {

        var v2;
        v2 = 10;
        let l2;
        l2 = 20;
        // You must specify its value in the same statement in which its declared 
        const c2 = 30;

        console.log(`var   2: ${++v2}`);
        console.log(`let   2: ${++l2}`);
        console.log(`const 2: ${++c2}`);

    } catch (e) {
        console.log(`${e.name} - ${e.message}`);
    }


    // Const with Arrays

    const name = [];
    name.push('pikachu');
    name.push('milotic');
    console.log(name)

    const pokemon = {
        name: 'Pikachu'
    };
    pokemon.name = 'Milotic' // this will work ! person variable is not completely reassigned, but mutated
    console.log(pokemon.name) // "Milotic"
    pokemon = "Kingler" // raises an error, because reassignment is not allowed with const declared variables

})();