Use array functions with async callbacks

array_promises.js

/**
 * A simple promise generator that waits for n seconds and returns a promise that resolves to n.
 */
function wait(n) {
    return new Promise(resolve => setTimeout(resolve.bind(null, n), n * 1000));
}

/**
 * A simple function that invokes promise and displays the result.
 */
async function simplePromise() {
    console.log("Before wait(3)");
    console.log(await wait(3));
    console.log("After wait(3)");
}

/**
 * A sample function that uses Promise.all to collect values in a array map function with async call back.
 */
async function async_map() {
    const arr = [1,2,3];
    console.log("Before map");
    console.log(await Promise.all(arr.map(async x => {
        return await wait(x);
    })));
    console.log("After map");
}

/**
 * A sample function that adds a new Array function to collect values in a array reduce style function.
 */
async function async_reduce() {
    const arr = [1,2,3];
    console.log("Before reduce");
    console.log(await arr.areduce(async (prev, x) => {
        return prev + await wait(x);
    }, 0));
    console.log("After reduce");
}

// simplePromise();
// async_map();

Array.prototype.areduce = async function(cb, initial) {
    let result = initial;
    for(let i=0; i< this.length; i++) {
        result = await cb(result, this[i]);
    }
    return result;
}

async_reduce();