pcre2-wasm

PCRE2 (Perl Compatible Regular Expressions) compiled to WebAssembly for use in the browser.

Installation

npm install @ofjansen/pcre2-wasm

Usage

Internally this module uses the PCRE2 library, running in a WebAssembly instance. This has a side effect of requiring you do a few unusual things when using this module:

Initialization

Before calling any constructors or methods, you must first asynchronously initialize the module by calling init.

import libpcre2 from '@ofjansen/pcre2-wasm';

async function main () {
  const lib = libpcre2();
  lib.PCRE.init();
  // make other PCRE calls...
}

main()

Memory Management

When you create a new PCRE instance, you are allocating memory within the WebAssembly instance. Currently, there are no hooks in JavaScript that let us automatically free this memory when the PCRE instance is garbage collected by the JavaScript runtime. This means that in order to prevent memory leaks, you must call .destroy() on a PCRE instance when it is no longer needed.

API

import libpcre2 from '@ofjansen/pcre2-wasm';

const lib = libpcre2();

PCRE.init()

Initializes the module, returning a Promise that is resolved once initialization is complete. You must call this at least once and await the returned Promise before calling any other PCRE methods or constructors.

PCRE.version()

Returns a string with the PCRE2 version information.

new PCRE(pattern, flags)

Creates a new PCRE instance, using pcre2_compile() to compile pattern, using flags as the compile options. You must call .destroy() on the returned instance when it is no longer needed to prevent memory leakage.

• pattern: A string containing a Perl compatible regular expression. Tip: use String.raw to avoid needing to escape backslashes.
• flags: An optional string with each character representing an option. Supported flags are i, m, s, and x. See perlre for details.

const pattern = String.raw`\b hello \s* world \b`
const re = new PCRE(pattern, 'ix')

// ...

re.destroy()

In the event of a compilation error in the pattern or an unsupported flag, an Error will be thrown with an error message from PCRE2. Additionally, it will have an offset property indicating the character offset in pattern where the error was encountered.

let re

try {
  re = new PCRE(String.raw`a)b`)
}
catch (err) {
  console.error(`Compilation failed: ${err.message} at ${err.offset}.`)
  // Prints: Compilation failed: unmatched closing parenthesis at 1.
}

re.destroy()

Releases the memory allocated in the WebAssembly instance. You must call this method manually once you no longer have a need for the instance, or else your program will leak memory.

re.match(subject, startOffset?)

Match the subject against the regular expression, starting at startOffset if specified (otherwise, start at position 0).

match output

Returns an object that lists numbered and named captures, each with a start, end, and match field.

For example, matching 000123 against /^(?<leading_zeros>0+).*$/ would result in the following object:

{
  length: 1,
  0: { start: 0, end: 6, match: "000123" },
  1: { start: 0, end: 4, match: "000" },
  leading_zeros: { start: 0, end: 4, match: "000" }
}

On no match, returns null.

On an error, throws an Error object whose string is a PCRE2 error name from PCRE2.h.

re.matchAll(subject, startOffset?)

Returns an array of re.match() results.

On no match, returns an empty array [].

On an error, throws an Error object whose string is a PCRE2 error name from PCRE2.h.

re.substitute(subject, replacement, startOffset?)

Performs a single substitution on subject against the regular expression, using replacement, starting at startOffset if specified (otherwise 0).

Returns a string.

On an error, throws an Error object whose string is a PCRE2 error name from PCRE2.h.

re.substituteAll(subject, replacement, startOffset?)

Performs all substitutions on subject against the regular expression, using replacement, starting at startOffset if specified (otherwise 0).

Returns a string.

On an error, throws an Error object whose string is a PCRE2 error name from PCRE2.h.

re.exec(subject, global?)

If global is specified and is truthy, will execute matchAll(); otherwise executes match().

Contributing

Prerequisites for development include Docker, make, and curl. All emscripten compiles (via emcc) are done in docker containers to control the build environment.

Credits

This is a fork of stephen-riley/pcre2-wasm, with minor adjustments to make it work in a browser application I'm working on.