UXP for ExtendScript Developers

If you're coming to UXP from ExtendScript and the ESTK (ExtendScript ToolKit) or its successor, the ExtendScript Debugger, here's what's new.

ExtendScript wasn't unique to Photoshop, so most of what follows (modern JavaScript, development environment, UI, HTML support) applies no matter which host application you're moving from. The DOM access section below uses Photoshop as its example since that's the most common source of ExtendScript migrations; see the Host Apps menu at the top of this site for your host application's own DOM API reference if you're migrating from a different one. The batchPlay API and migration helper shown below are Photoshop-specific.

Different DOM access

UXP provides different methods for accessing each host application's DOM. See your host's API reference for details. The entire DOM isn't yet exposed through UXP for every host application, but coverage grows with each release.

In Photoshop, batchPlay can access operations not exposed directly by the Photoshop DOM API. batchPlay is not available in Premiere, InDesign, or Media Encoder.

A Photoshop migration helper for ExtendScript developers

If you use executeAction and executeActionGet often in Photoshop ExtendScript code, the ExtendScript batchPlay logger utility can help. Plug the ps-es-to-uxp JSX code into your ExtendScript project, and it prints out your executeAction and executeActionGet calls in a format suitable for batchPlay.

Development environment

ExtendScript Toolkit ("ESTK") was the development environment of choice for many years. It has largely been replaced by a Visual Studio Code extension, a widely used editor.

UXP source code (HTML, CSS, and JavaScript) can be developed in the editor of your choice, though many UXP developers prefer VS Code for its extensibility.

User interface

Many ExtendScript scripts have little to no UI: the end user picks a script from a menu, and it runs without a visible interface. When an ExtendScript script does need a UI, it typically uses simple alert(), confirm(), and prompt() calls, or the more full-featured ScriptUI.

In UXP, you design as simple or as complex a UI as you want, using HTML and CSS for the visual part and JavaScript for the logic behind it.

Modern JavaScript

ExtendScript uses an old version of JavaScript (ES3). UXP uses the V8 JavaScript engine, which supports ES6 and a number of features ExtendScript lacks. As an ExtendScript developer, you'll want to be familiar with modern ECMAScript syntax to follow UXP sample code. At minimum, it helps to understand:

• const and let declarations, versus var
• Promises and asynchronous functions
• Anonymous functions
• Arrow functions
• Template literals
• Maps

What's different in UXP's HTML support

UXP provides an HTML interpreter similar to Chromium, but more limited than a full browser, so some common web CSS and HTML idioms don't work. See the common Unsupported Elements and Unsupported Attributes reference for the current list, which applies across every UXP host.