JavaScript promises are commonly used in scenarios where you need to work with asynchronous operations, such as making HTTP requests, reading files, or interacting with databases. They provide a cleaner and more structured way to handle asynchronous code compared to traditional callback functions.
Promise chaining is a technique that allows you to execute asynchronous operations in a sequential and readable manner. It involves chaining multiple promises together, where each subsequent promise depends on the result of the previous one.
fetch('https://api.example.com/data') // Make a network request
.then(response => response.json()) // Parse JSON response
.then(data => {
// Process the data
console.log(data.name);
return data.id; // Return the ID for the next step
})
.then(id => {
// Perform another operation using the ID
fetch(`https://api.example.com/details/${id}`)
.then(response => response.json())
.then(details => {
console.log(details.description);
})
.catch(error => {
console.error("Error fetching details:", error);
});
})
.catch(error => {
console.error("Error fetching data:", error);
});The .then() method is used to handle the fulfillment of the promise, you typically return either a value or a new Promise. If the operation is synchronous, return a value; if it’s asynchronous, return a new Promise. This distinction allows you to handle both types of operations seamlessly within a Promise chain.
the .catch() method is used to handle any errors or rejections. It is typically added at the end of a series of .then() calls. If any of the preceding promises in the chain encounters an error (i.e., if it is rejected), the control will be passed to the nearest .catch() block, allowing you to handle and log the error or take any necessary corrective actions.