Promises are an integral part of asynchronous programming in JavaScript. They allow us to handle operations that may take some time to complete, such as fetching data from an API or reading from a file. However, there are scenarios where we need to handle promises conditionally, based on certain conditions. In this blog post, we will explore different techniques to handle conditional promises in JavaScript.

Table of Contents

• Introduction to Promises
• Handling Conditional Promises
  • Using if statements
  • Using Promise.all
  • Using async/await
• Conclusion

Introduction to Promises

Promises in JavaScript are objects that represent the eventual completion or failure of an asynchronous operation. They have three possible states: pending, fulfilled, or rejected. The then() method of a promise is used to handle the fulfillment, while the catch() method is used to handle any errors or rejections.

fetch('https://api.example.com/data')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error(error));

In the above example, we are fetching data from an API using the fetch() function. The returned promise is chained with then() to parse the response as JSON and log the data to the console. If there is an error, it is caught and logged using catch().

Handling Conditional Promises

There are multiple ways to handle conditional promises in JavaScript, depending on the specific requirements of your code.

Using if statements

The simplest way to handle conditional promises is by using if statements. You can conditionally execute different promises based on a condition.

if (condition) {
  fetch('https://api.example.com/data')
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error(error));
} else {
  // Perform another operation
}

In the above example, if the condition is true, the API call is made and the data is logged. Otherwise, you can perform another operation based on the condition.

Using Promise.all

If you have multiple promises that need to be conditionally handled, you can use Promise.all to wait for all promises to resolve and then handle them collectively.

const promises = [];

if (condition1) {
  promises.push(fetchPromise1);
}

if (condition2) {
  promises.push(fetchPromise2);
}

Promise.all(promises)
  .then(results => {
    // Handle the results
  })
  .catch(error => console.error(error));

In the above example, Promise.all is used to wait for all promises in the promises array to resolve. Then, the then() method is used to handle the results collectively. If any of the promises reject, the catch() method is called.

Using async/await

Another approach to handling conditional promises is by using async/await syntax, which allows writing asynchronous code in a synchronous manner.

async function fetchData() {
  if (condition) {
    try {
      const response = await fetch('https://api.example.com/data');
      const data = await response.json();
      console.log(data);
    } catch (error) {
      console.error(error);
    }
  } else {
    // Perform another operation
  }
}

In the above example, the fetchData() function is an async function that uses await to wait for the resolution of promises. The code inside the try block is executed if the condition is true. If there is an error, it is caught and logged using catch().

Conclusion

Handling conditional promises in JavaScript can be done using various techniques, such as if statements, Promise.all, or async/await. Choose the approach that best fits your specific requirements and coding style. Promises provide a powerful mechanism for handling asynchronous operations, and mastering the techniques to handle them conditionally will significantly improve your JavaScript code.