How to wait for a promise to finish before returning the variable of a function ?

// Returns a promise that resolves after `ms` milliseconds
const wait = ms => new Promise(resolve => setTimeout(resolve, ms));

// Logs failure message
function failureCallback() {
    console.log("This is failure callback");
}

// Waits 4 seconds, then logs and throws an error
wait(4 * 1000).then(() => {
    console.log("waited for 4 seconds");
    throw new Error("error occurred");
}).catch(() => {
    failureCallback(); // Handles the error
});

// Waits 2 seconds, then logs message
wait(2 * 1000).then(() => 
    console.log("waited for 2 seconds"));

// This function returns promise after 2 seconds
let first_function = function () {
    console.log("Entered first function");
    return new Promise(resolve => {
        setTimeout(function () {
            resolve("\t\t This is first promise");
            console.log("Returned first promise");
        }, 2000);
    });
};

// This function executes returns promise after 4 seconds
let second_function = function () {
    console.log("Entered second function");
    return new Promise(resolve => {
        setTimeout(function () {
            resolve("\t\t This is second promise");
            console.log("Returned second promise");
        }, 4000);
    });
};

let async_function = async function () {
    console.log('async function called');

    const first_promise = await first_function();
    console.log("After awaiting for 2 seconds," +
        "the promise returned from first function is:");
    console.log(first_promise);

    const second_promise = await second_function();
    console.log("After awaiting for 4 seconds, the" +
        "promise returned from second function is:");
    console.log(second_promise);
}

async_function();