Using TypeScript with async await operators, promises, and the memoization pattern

Question

Using TypeScript with async await operators, promises, and the memoization pattern

I am currently in the process of updating my code to incorporate the latest TypeScript enhancements. We have implemented various memoization patterns, with the main goal being to ensure that services with multiple subscribers wait for one call and do not trigger multiple calls simultaneously.
Here is a snippet of the code:

private isAdmin: Promise<Boolean>;
public IsCurrentUserAdmin(): Promise<Boolean> {
if (!this.isAdmin) {
this.isAdmin = httpService.goGetTheData().then((data) => //perform actions and return Boolean);
}
return this.isAdmin;

My query is: Will using something like this achieve the same result as with the await operator since I do not have direct access to the promise object?

public IsCurrentUserAdmin(): Promise<Boolean> {
const isAdminData = await httpService.goGetTheData();
// manipulate the data to obtain the desired value
return isAdmin;
}

typescript promise async-await memoization

Answer 1

Answer №1

It is essential to have access to the promise object for memoization. While using async/await may not prevent this, as it is essentially just a syntax shortcut for then calls, in your specific scenario, it may not be very helpful. This is because you are caching the promise returned by .then(…) instead of the initial goGetTheData() promise. To address this, you would need to create an additional helper method:

private isAdmin: Promise<boolean>;
private async fetchIsAdmin(): Promise<boolean> {
    const data = await httpService.goGetTheData();
    // Perform necessary operations and
    return // a boolean value
}
public IsCurrentUserAdmin(): Promise<boolean> {
    if (!this.isAdmin) {
        this.isAdmin = this.fetchIsAdmin();
    // You could also `await this.isAdmin` here, but that would result in waiting for every call
    return this.isAdmin;
}

Answer 2

It is essential to have access to the promise object for memoization. While using async/await may not prevent this, as it is essentially just a syntax shortcut for then calls, in your specific scenario, it may not be very helpful. This is because you are caching the promise returned by .then(…) instead of the initial goGetTheData() promise. To address this, you would need to create an additional helper method:

private isAdmin: Promise<boolean>;
private async fetchIsAdmin(): Promise<boolean> {
    const data = await httpService.goGetTheData();
    // Perform necessary operations and
    return // a boolean value
}
public IsCurrentUserAdmin(): Promise<boolean> {
    if (!this.isAdmin) {
        this.isAdmin = this.fetchIsAdmin();
    // You could also `await this.isAdmin` here, but that would result in waiting for every call
    return this.isAdmin;
}

Using TypeScript with async await operators, promises, and the memoization pattern

Answer №1

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