Friday, 23 August, 2019 UTC
Summary
Async can throw a real wrench into the cogs of our programming workflows, all despite the fact that async is the modern JavaScript pattern. While async/await helps, there’s sometimes confusion about the way to have a single function that returns a value whether it exists or needs a Promise to retrieve.
The key thing to remember is that functions declared as
async automatically return a Promise, so you don’t need explicity return the existing content with Promise.resolve(content):async function getValueOrFetch(ojbOrInfo) {
// If the value exists, immediately return it
if(ojbOrInfo) {
return ojbOrInfo;
}
// Return the promise-based info
return asyncFunctionToGetInfo(ojbOrInfo);
}
Let’s look at a real life example: returning cached contents instead of doing a
fetch call to retrieve them:const cache = {
/* url: content */
};
// Async function that returns cached content or retrieves fresh content
async function getInfo(url) {
// Check for value in cache
if (cache[url]) {
// Return the content, no need for Promise.resolve
return cache[url];
}
// Get the content fresh
const content = await fetch("https://www.facebook.com").then(r => r.text());
cache[url] = content;
return content;
}
My main goal with this post is making you understand that
return Promise.resolve(data) isn’t needed with async functions — you can simply return the value and it will be wrapped in a promise!The post Promises and Static Values appeared first on David Walsh Blog.