JS await pitfall

index.js

let result = 0;

const sleep = (ms) => new Promise((resolve)=>{
    setTimeout(resolve, ms);
});

const mult = async(val) => {
    await sleep(200);
    return val * val;
}

const add = async(val)=>{
    result += await mult(val);
}

Promise.all([
    add(2),
    add(1),
]).then(()=>{
    console.log(result); // prints 1
});