Asynchronous programming is a popular programming paradigm that allows for efficient code execution by avoiding blocking calls. In this article, we'll take a look at how to work with asynchronous programming in TypeScript and Node.js.
Asynchronous programming is a programming paradigm that allows for efficient code execution by avoiding blocking calls. Blocking calls are calls that wait for a response before continuing execution, which can cause performance issues.
With asynchronous programming, a program can continue executing other code while waiting for a response from a blocking call. This allows for more efficient code execution, as the program is not waiting idly for a response.
TypeScript is a typed superset of JavaScript that compiles to clean, simple JavaScript code. It offers classes, modules, and interfaces to help you build robust components.
TypeScript is designed for development of large applications and transcompiles to JavaScript. Asynchronous programming is a popular programming paradigm in TypeScript, as it allows for efficient code execution by avoiding blocking calls.
There are two ways to work with asynchronous programming in TypeScript: Promises and async/await.
Promises are a way to work with asynchronous code in TypeScript. A promise represents an operation that hasn't completed yet, but is expected to in the future.
Promises are used to handle asynchronous operations in TypeScript. A promise can be in one of three states:
A promise can be created using the Promise
constructor:
const promise = new Promise((resolve, reject) => {
// do something async
});
The Promise
constructor takes a callback function with two parameters: resolve
and reject
. The resolve
function is called when the asynchronous operation completes successfully. The reject
function is called when the asynchronous operation fails.
Once a promise is created, you can use the then()
method to register a callback function to be called when the promise is fulfilled:
promise.then((result) => {
// do something with the result
});
You can also use the catch()
method to register a callback function to be called when the promise is rejected:
promise.catch((error) => {
// do something with the error
});
Here's an example of using a promise to load a image from a URL:
const loadImage = (url: string): Promise<string> => {
return new Promise((resolve, reject) => {
const image = new Image();
image.onload = () => resolve(url);
image.onerror = () => reject(new Error(`Failed to load image from URL: ${url}`));
image.src = url;
});
};
In this example, we create a Promise
that resolves with the image URL when the image has loaded, or rejects with an error if the image fails to load.
Async/await is a way to work with asynchronous code in TypeScript. It allows you to write asynchronous code that looks and feels like synchronous code.
Async/await is built on top of promises and uses async
and await
keywords.
The async
keyword is used to create an asynchronous function. An asynchronous function is a function that returns a promise:
async function loadImage(url: string): Promise<string> {
// do something async
}
The await
keyword is used to wait for a promise to be resolved. It can only be used inside an async
function:
async function loadImage(url: string): Promise<string> {
const image = await loadImage(url);
// do something with the image
}
In this example, we use the async
keyword to create an asynchronous function. We use the await
keyword to wait for the loadImage
function to be resolved.
Async/await is a popular way to work with asynchronous code in TypeScript, as it allows you to write asynchronous code that looks and feels like synchronous code.
Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.
Node.js is designed for building scalable network applications. Asynchronous programming is a popular programming paradigm in Node.js, as it allows for efficient code execution by avoiding blocking calls.
There are two ways to work with asynchronous programming in Node.js: callbacks and promises.
Callbacks are a way to work with asynchronous code in Node.js. A callback is a function that is called when an asynchronous operation completes.
When an asynchronous operation is started, a callback function is provided. The callback function is called when the asynchronous operation completes.
Callback functions are commonly used in Node.js for asynchronous operations such as file I/O.
Here's an example of using a callback function to read a file:
const fs = require('fs');
fs.readFile('/path/to/file', (err, data) => {
if (err) {
// do something with the error
} else {
// do something with the data
}
});
In this example, we use the fs.readFile
function to read a file. The fs.readFile
function takes a path to a file and a callback function. The callback function is called with an err
and data
parameters. If the err
parameter is not null
, then an error occurred. Otherwise, the data
parameter contains the data from the file.
Promises are a way to work with asynchronous code in Node.js. A promise represents an operation that hasn't completed yet, but is expected to in the future.
Promises are used to handle asynchronous operations in Node.js. A promise can be in one of three states:
A promise can be created using the Promise
constructor:
const promise = new Promise((resolve, reject) => {
// do something async
});
The Promise
constructor takes a callback function with two parameters: resolve
and reject
. The resolve
function is called when the asynchronous operation completes successfully. The reject
function is called when the asynchronous operation fails.
Once a promise is created, you can use the then()
method to register a callback function to be called when the promise is fulfilled:
promise.then((result) => {
// do something with the result
});
You can also use the catch()
method to register a callback function to be called when the promise is rejected:
promise.catch((error) => {
// do something with the error
});
Here's an example of using a promise to load an image from a URL:
const loadImage = (url: string): Promise<string> => {
return new Promise((resolve, reject) => {
const image = new Image();
image.onload = () => resolve(url);
image.onerror = () => reject(new Error(`Failed to load image from URL: ${url}`));
image.src = url;
});
};
In this example, we create a Promise
that resolves with the image URL when the image has loaded, or rejects with an error if the image fails to load.
Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.
Node.js is designed for building scalable network applications. Asynchronous programming is a popular programming paradigm in Node.js, as it allows for efficient code execution by avoiding blocking calls.
There are two ways to work with asynchronous programming in Node.js: callbacks and promises.
Callbacks are a way to work with asynchronous code in Node.js. A callback is a function that is called when an asynchronous operation completes.
When an asynchronous operation is started, a callback function is provided. The callback function is called when the asynchronous operation completes.
Callback functions are commonly used in Node.js for asynchronous operations such as file I/O.
Here's an example of using a callback function to read a file:
const fs = require('fs');
fs.readFile('/path/to/file', (err, data) => {
if (err) {
// do something with the error
} else {
// do something with the data
}
});
In this example, we use the fs.readFile
function to read a file. The fs.readFile
function takes a path to a file and a callback function. The callback function is called with an err
and data
parameters. If the err
parameter is not null
, then an error occurred. Otherwise, the data
parameter contains the data from the file.
Promises are a way to work with asynchronous code in Node.js. A promise represents an operation that hasn't completed yet, but is expected to in the future.
Promises are used to handle asynchronous operations in Node.js. A promise can be in one of three states:
A promise can be created using the Promise
constructor:
const promise = new Promise((resolve, reject) => {
// do something async
});
The Promise
constructor takes a callback function with two parameters: resolve
and reject
. The resolve
function is called when the asynchronous operation completes successfully. The reject
function is called when the asynchronous operation fails.
Once a promise is created, you can use the then()
method to register a callback function to be called when the promise is fulfilled:
promise.then((result) => {
// do something with the result
});
You can also use the catch()
method to register a callback function to be called when the promise is rejected:
promise.catch((error) => {
// do something with the error
});
Here's an example of using a promise to load an image from a URL:
const loadImage = (url: string): Promise<string> => {
return new Promise((resolve, reject) => {
const image = new Image();
image.onload = () => resolve(url);
image.onerror = () => reject(new Error(`Failed to load image from URL: ${url}`));
image.src = url;
});
};
In this example, we create a Promise
that resolves with the image URL when the image has loaded, or rejects with an error if the image fails to load.