Custom Promises and Asynchronous Programming in SuiteScript

TL;DR

Custom promises allow SuiteScript developers to handle asynchronous operations smoothly by providing a framework that represents results of an asynchronous process. Leveraging custom promises improves code readability and efficiency, particularly in client and server scripting.

What Are Promises?

A promise in JavaScript is an object that signifies the eventual result of an asynchronous operation. When created, it serves as a placeholder for the success or failure of that operation.

Promises can hold one of the following states:

• fulfilled: indicates a successful operation.
• rejected: indicates a failed operation.
• pending: indicates the operation is still ongoing.

Initially, a promise starts in the pending state. Once the asynchronous process completes, the promise transitions to either fulfilled or rejected, preventing further state changes afterwards. SuiteScript 2.x integrates promise APIs that support the asynchronous nature of scripting, enhancing code manageability.

Using Promises in SuiteScript

SuiteScript 2.x provides built-in promise APIs that client scripts can leverage. As of NetSuite version 2021.1, a subset of server scripts supports promises as well. Here are a few best practices and considerations for implementing promises in your SuiteScript code:

• Use .catch to handle promise rejections instead of offering a second argument to .then.
• Maintain short promise chains to optimize memory and CPU usage.
• Utilize promise.all when dealing with multiple independent asynchronous calls.
• Make use of promise.finally for any cleanup code needed regardless of the promise outcome.

Consider employing the async and await keywords alongside promises for enhanced readability and maintainability.

Custom Promises Example

Custom promises extend the ability to handle asynchronous operations beyond the built-in SuiteScript promise APIs. Below is an example of creating a custom promise using the native Promise object in JavaScript:

1/**
2* @NApiVersion 2.x
3*/
4 
5define(function(){
6    function doSomething(addresses){
7        var promise = new Promise(function(resolve, reject){
8            var url = 'https://your.favorite.maps/api/directions?start=' + addresses.start + '&end=' + addresses.end,
9                xhr = new XMLHttpRequest();
10 
11                xhr.addEventListener('load', function () {
12                    if (xhr.status === 200) {
13                        resolve(xhr.responseText);
14                    } else {
15                        reject(xhr.statusText);
16                    }
17                });
18 
19                xhr.addEventListener('error', function () {
20                    reject(xhr.statusText);
21                });
22 
23                xhr.open('GET', url, true);
24                xhr.send();
25            });
26 
27        return promise;
28    }
29 
30    return {
31        lookupDirections: doSomething
32    };
33});

This code offers a robust template for performing asynchronous tasks while ensuring that errors are adequately managed, exemplifying how to create and use custom promises.

Conclusion

Leveraging custom promises in NetSuite's SuiteScript enhances your ability to manage asynchronous processes effectively. Implementing best practices in promise usage not only leads to cleaner code but also ensures robust error handling, thus improving overall application performance.

Key Takeaways

• A promise is a key JavaScript concept for managing asynchronous operations.
• SuiteScript 2.x provides built-in promise APIs facilitating easier asynchronous coding.
• Custom promises offer flexibility beyond built-in APIs, enabling tailored asynchronous functionality.
• Following best practices leads to cleaner, more efficient code.