regexp-match-indices

This package provides a polyfill/shim for the RegExp Match Indices proposal.

The implementation is a replacement for RegExp.prototype.exec that approximates the beahvior of the proposal. Because RegExp.prototype.exec depends on a receiver (the this value), the main export accepts the RegExp to operate on as the first argument.

Installation

npm install regexp-match-indices

Usage

Standalone

const execWithIndices = require("regexp-match-indices");
 
const text = "zabbcdef";
const re = new RegExp("ab*(cd(?<Z>ef)?)");
const result = execWithIndices(re, text);
console.log(result.indices);    // [[1, 8], [4, 8], [6, 8]]

Shim

require("regexp-match-indices").shim();
// or
require("regexp-match-indices/shim")();
// or
require("regexp-match-indices/auto");
 
const text = "zabbcdef";
const re = new RegExp("ab*(cd(?<Z>ef)?)");
const result = re.exec(re, text);
console.log(result.indices);    // [[1, 8], [4, 8], [6, 8]]

Configuration

The polyfill can be run in two modes: "lazy" (default) or "spec-compliant". In "spec-compliant" mode, the indices property is populated and stored on the result as soon as exec() is called. This can have a significant performance penalty for existing RegExp's that do not use this feature. By default, the polyfill operates in "lazy" mode, where the indices property is defined using a getter and is only computed when first requested.

You can specify the configuration globally using the following:

require("regexp-match-indices").config.mode = "spec-compliant"; // or "lazy"
// or
require("regexp-match-indices/config").mode = "spec-compliant"; // or "lazy"