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JavaScript environment

This page describes PopClip's JavaScript environment, in which JavaScript actions and module-based extensions run.


PopClip's JavaScript engine is Apple's JavaScriptCore, which is part of macOS.

JavaScriptCore's language and standard library support varies depending on macOS version. However, PopClip uses core-js to provide polyfills for the JavaScript standard library up to ES2023. You can also assume availability of language features up to ES2017 on all macOS versions that PopClip supports.

PopClip also has built-in support for TypeScript. See TypeScript support.

Language reference

The JavaScript language reference I use and recommend is MDN.

PopClip globals

PopClip provides a global object, popclip, and other globals, which are documented in detail in the JavaScript API Reference. The following is a summary of the commonly needed parts.

Global popclip object

Scripts can access the selected text and other input via the following readonly properties of the popclip global:

  • popclip.input.text: the full plain text selection
  • popclip.input.matchedText: the part of the text matching the requirement or regex
  • popclip.input.regexResult: if regex was specified, this is an array containing the full result of the match, including any capture groups
  • popclip.input.html: the html backing the selection (if capture html is set)
  • popclip.input.markdown: the markdownified html (if capture html is set)
  • array of detected web URLs
  • popclip.context.browserUrl, popclip.context.browserTitle: browser page URL and title, if available.
  • popclip.modifiers.command, popclip.modifiers.option, popclip.modifiers.shift, popclip.modifiers.control: booleans for modifier keys pressed
  • popclip.options: an object with properties for each option, where the property name is the option's identifier. Option values can be either strings or booleans

Scripts can perform actions via calling methods on the popclip global:

Global pasteboard object

Scripts can also access the macOS clipboard directly, via the pasteboard global:

  • pasteboard.text - the current plain text content of the clipboard, a read/write property.

Other globals

There is also a global function print() for debug output, and a global require() function.

Using require()

PopClip has a require() function for loading modules and JSON data from other files. It takes a single string argument, interpreted as follows:

  • If the string starts with ./ or ../, it is interpreted as a path to a file in the package directory, relative the current file.
  • Otherwise, the string is interpreted as a path relative to the root of the package directory.
  • If no file is found in the package directory, the string is then checked against the names of the bundled libraries. If found, the library module is loaded and returned.

Results are cached, and subsequent calls to require() with the same argument will return the same object instance that was returned the first time.

File paths beginning with / or using .. to go up a directory level outside the package directory are not valid.

Supported file types

The require() function can load the following file types:

File extensionDescription
.jsA JavaScript module in CommonJS format.
.tsA TypeScript module. TypeScript modules may use ES Modules syntax.
.jsonA JSON file parsed into a JavaScript object.

If no file name extension is specified, PopClip will try .js, .ts, .json in order.

Return value

The return value of require() is the exported value of the module, or the parsed JSON object. If the specified file or library module is not found, or an invalid path is supplied, undefined is returned.

Bundled libraries

Some libraries from NPM are bundled within the PopClip app itself, and are available to load by scripts. These are:

axios1.5.0HTTP client
case-anything2.1.13Case conversion library
content-type1.0.5Parse HTTP Content-Type header
dom-serializer2.0.0HTML serializer
entities4.5.0HTML entity encoder/decoder
htmlparser28.0.2HTML parser
js-yaml4.1.0YAML parser
linkedom0.15.0DOM implementation
linkifyjs4.1.1Detect web links in text
rot13-cipher1.0.0ROT13 cipher
sanitize-html2.11.0HTML sanitizer
turndown7.1.2HTML to Markdown converter
typescript5.2.2TypeScript transpiler & tools

Library modules may be loaded by name, for example:

const axios = require("axios");
import axios from "axios";

Asynchronous operations and async/await

PopClip provides implementations of XMLHttpRequest and setTimeout, which are asynchronous. If a script uses these, PopClip will show its spinner and wait until the last asynchronous operation has finished. During asynchronous operations, clicking PopClip's spinner will cancel all current operations.

The returned value from the script (if any) is the return value of the last function to complete. For example:

// # popclip setTimeout example
// name: setTimeout Test
// after: show-result
// language: javascript
setTimeout(() => {
  return "bar";
}, 1000); // 1 second delay
return "foo";
// result shown will be 'bar', not 'foo'

Your functions can be async, and you can use the await keyword when calling any function that returns a Promise. PopClip handles the details of resolving promises internally.

As a convenience, PopClip supplies a global function sleep() as a promise-based wrapper around setTimeout():

// # popclip await example
// name: Await Test
// language: js
await sleep(5000); // 5 second delay

Network access from JavaScript

Entitlement needed

To use XHR, the network entitlement must be present in the entitlements array in the extension's config.

PopClip provides its own implementation of XMLHttpRequest (XHR). This is the only way for JavaScript code to access the network.

PopClip is also bundled with the HTTP library axios, which is an easier to use wrapper around XHR.

Due to macOS's App Transport Security, PopClip can only access https: URLs. Attempts to access http: URLs will throw a network error.

Here's an example extension snippet that downloads a selected URL's contents, and copies it to the clipboard:

// # popclip JS network example
// name: Download Text
// icon: symbol:square.and.arrow.down.fill
// requirements: [url]
// entitlements: [network]
// after: copy-result
// language: javascript
const axios = require("axios");
const response = await axios.get([0]);
/* note: there is no particular need to check the return status here.
   axios calls will throw an error if the HTTP status is not 200/2xx. */
// # popclip TS network example
// name: Download Text
// icon: symbol:square.and.arrow.down.fill
// requirements: [url]
// entitlements: [network]
// after: copy-result
// language: typescript
import axios from "axios";
const response = await axios.get([0]);
/* note: there is no particular need to check the return status here.
   axios calls will throw an error if the HTTP status is not 200/2xx. */

For a more substantial axios example, see for example Instant Translate.

TypeScript support

PopClip has built-in support for TypeScript. You can supply TypeScript source in any place where a JavaScript file can be specified. PopClip loads files with a .js extension as raw JavaScript, and loads files with a .ts extension as TypeScript.

At load time, PopClip transpiles TypeScript files into JavaScript source. PopClip does not do any type validation on the TypeScript source.

PopClip ships with a TypeScript type definitions file, popclip.d.ts, to assist in developing extensions. This will enable autocomplete and type-checking in TypeScript-aware editors such as VS Code. So that your editor can find the type definitions, you can reference the definitions file in your TypeScript code using a triple-slash directive at the top of the file, like this:

/// <reference path="/Applications/" />
/// <reference path="/Applications/Setapp/" />

JavaScript testing

PopClip has a 'test harness' mode, which runs JavaScript files in the PopClip environment from the command line. It is useful for running unit tests of your code in PopClip's environment, with the same libraries, globals etc. It is activated by calling PopClip's executable (inside the package) with the parameter runjs followed by the file name to run.

/Applications/ runjs test.js

Some notes:

  • When running in the test harness, the popclip global is not available.
  • Scripts can output strings with the global print() function (not console.log()).
  • Scripts running in the test harness always have the network access entitlement.
  • The test harness is a somewhat experimental feature at present. Please reach out to me if something does not seem to work as expected.