In the realm of JavaScript, managing asynchronous operations has traditionally been a challenge. Promises and generators introduced a more elegant way to handle asynchronous code, and with a touch of creativity, developers have created utilities to enhance this experience. In this blog post, we'll explore a concise utility function called asynq
that leverages generators to simulate asynchronous behavior.
The await Operator:
The await
operator in JavaScript is used in an async
function to pause execution until a Promise is resolved or rejected. It allows asynchronous code to be written in a more synchronous fashion, making it easier to work with Promises.
Here a small example of how modern await
operator can be used:
async function getData() {
const response = await fetch("https://jsonplaceholder.typicode.com/todos/1");
const data = await response.json();
}
Previous snippet fetches data from a server and stores the parsed JSON response in the variable, leveraging the async/await syntax for handling asynchronous operations more elegantly.
The asynq
Utility:
Let's dive into the code snippet that defines the asynq
utility:
function asynq(promise) {
const generator = promise();
(function next(value) {
const it = generator.next(value);
if (it.done) {
return it.value;
} else {
return Promise.resolve(it.value).then(next);
}
})();
}
The asynq
function takes a promise as an argument, creating a generator by invoking it. The magic happens inside the immediately-invoked function expression (IIFE) named next
.
This function recursively processes the generator's values until completion, effectively simulating asynchronous iteration.
Usage Example with getData
:
Let's see asynq
in action with a practical example:
function* getData() {
const data1 = yield 1;
console.log(data1);
const data2 = yield new Promise((resolve) => {
resolve(2);
});
console.log(data2);
const response = yield fetch("https://jsonplaceholder.typicode.com/todos/1");
const data3 = yield response.json();
console.log(data3);
}
asynq(getData);
In this getData
generator function, we witness the power of asynq
. It gracefully handles both synchronous and asynchronous values. The generator yields integers, Promises, and even the result of a fetch
call, showcasing the flexibility of this utility.
Wrapping it Up
JavaScript's native async/await syntax, widely adopted for its readability and ease of use, is intricately connected to the concept of generators.
The asynq
utility we explored in this article opens a little window into how await
operator works internally.
The await
operator is exclusive to async
functions. Same way as yield
operator is exclusive to generator functions.
Attempting to use await
outside of an async
function results in a syntax error. Same as using yield
operator outside of a generator function results in a syntax error too.
Try out asynchronous code with asynq
utility and in doing so, uncover the similarities between generators and asynchronous code with async/await that propels modern javascript
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