Memoize an async function by storing its results

asyncMemoize.js

function defaultHasher() {
    return JSON.stringify(arguments);
}

function asyncMemoize(fn, hasher=defaultHasher) {
    async function memozie() {
        let cache = memozie.cache;
        const key = hasher(arguments);

        if (!cache.hasOwnProperty(key)) {
            cache[key] = await fn.apply(this, arguments);
        }

        return cache[key];
    }

    memozie.cache = {};

    return memozie;
}

test.js

// test
function fetch(data) {
    return new Promise((resolve) => {
        setTimeout(function () {
            resolve(data)
        }, 1000)
    })
}

const fetchMemoize = asyncMemoize(fetch);

const now = Date.now();
fetchMemoize('user').then(function() {
    console.log(`fetch user cost time ${Date.now() - now}`);
    let current = Date.now();

    fetchMemoize('user').then(function() {
        console.log(`fetch user cost time ${Date.now() - current}`);
    })
})

fetchMemoize('role').then(function() {
    console.log(`fetch role cost time ${Date.now() - now}`);
})