let vs var: hoisting explained

function helloFunction() {
    console.log(hello);
    var hello = "e";
}

// This will work because of hoisting. The preprocessor will move up the var/let statement while compiling, like this:

function helloFunction() {
    var hello;
    console.log(hello);
    hello = "e";
}

// The difference between let and var is where they are hoisted. let hoists up to the last {, var hoists up to the last function begin.
// See those functions?
function varHello() {
    try {
        console.log(hello);
        var hello = "e";
    } catch {
        console.error("Error!");
    }
}

function letHello() {
    try {
        console.log(hello);
        let hello = "e";
    } catch {
        console.error("Error!");
    }
}

// That's how they'll be preprocessed:

function varHello() {
    var hello;
    try {
        console.log(hello);
        hello = "e";
    } catch {
        console.error("Error!");
    }
    delete hello;
}

function letHello() {
    try {
        let hello;
        console.log(hello);
        hello = "e";
        delete hello;
    } catch {
        console.error("Error!");
    }
}