PHP's xdiff_string_patch in JavaScript

Here’s what our current JavaScript equivalent to PHP's xdiff_string_patch looks like.

module.exports = function xdiff_string_patch (originalStr, patch, flags, errorObj) { // eslint-disable-line camelcase
// discuss at: https://locutus.io/php/xdiff_string_patch/
// original by: Brett Zamir (https://brett-zamir.me)
// improved by: Steven Levithan (stevenlevithan.com)
// note 1: The XDIFF_PATCH_IGNORESPACE flag and the error argument are not
// note 1: currently supported.
// note 2: This has not been tested exhaustively yet.
// note 3: The errorObj parameter (optional) if used must be passed in as a
// note 3: object. The errors will then be written by reference into it's `value` property
// example 1: xdiff_string_patch('', '@@ -0,0 +1,1 @@\n+Hello world!')
// returns 1: 'Hello world!'
// First two functions were adapted from Steven Levithan, also under an MIT license
// Adapted from XRegExp 1.5.0
// (c) 2007-2010 Steven Levithan
// MIT License
// <https://xregexp.com>
const _getNativeFlags = function (regex) {
// Proposed for ES4; included in AS3
return [
(regex.global ? 'g' : ''),
(regex.ignoreCase ? 'i' : ''),
(regex.multiline ? 'm' : ''),
(regex.extended ? 'x' : ''),
(regex.sticky ? 'y' : '')
].join('')
}
const _cbSplit = function (string, sep) {
// If separator `s` is not a regex, use the native `split`
if (!(sep instanceof RegExp)) {
// Had problems to get it to work here using prototype test
return String.prototype.split.apply(string, arguments)
}
const str = String(string)
const output = []
let lastLastIndex = 0
let match
let lastLength
const limit = Infinity
const x = sep._xregexp
// This is required if not `s.global`, and it avoids needing to set `s.lastIndex` to zero
// and restore it to its original value when we're done using the regex
// Brett paring down
const s = new RegExp(sep.source, _getNativeFlags(sep) + 'g')
if (x) {
s._xregexp = {
source: x.source,
captureNames: x.captureNames ? x.captureNames.slice(0) : null
}
}
while ((match = s.exec(str))) {
// Run the altered `exec` (required for `lastIndex` fix, etc.)
if (s.lastIndex > lastLastIndex) {
output.push(str.slice(lastLastIndex, match.index))
if (match.length > 1 && match.index < str.length) {
Array.prototype.push.apply(output, match.slice(1))
}
lastLength = match[0].length
lastLastIndex = s.lastIndex
if (output.length >= limit) {
break
}
}
if (s.lastIndex === match.index) {
s.lastIndex++
}
}
if (lastLastIndex === str.length) {
if (!s.test('') || lastLength) {
output.push('')
}
} else {
output.push(str.slice(lastLastIndex))
}
return output.length > limit ? output.slice(0, limit) : output
}
let i = 0
let ll = 0
let ranges = []
let lastLinePos = 0
let firstChar = ''
const rangeExp = /^@@\s+-(\d+),(\d+)\s+\+(\d+),(\d+)\s+@@$/
const lineBreaks = /\r?\n/
const lines = _cbSplit(patch.replace(/(\r?\n)+$/, ''), lineBreaks)
const origLines = _cbSplit(originalStr, lineBreaks)
const newStrArr = []
let linePos = 0
const errors = ''
let optTemp = 0 // Both string & integer (constant) input is allowed
const OPTS = {
// Unsure of actual PHP values, so better to rely on string
XDIFF_PATCH_NORMAL: 1,
XDIFF_PATCH_REVERSE: 2,
XDIFF_PATCH_IGNORESPACE: 4
}
// Input defaulting & sanitation
if (typeof originalStr !== 'string' || !patch) {
return false
}
if (!flags) {
flags = 'XDIFF_PATCH_NORMAL'
}
if (typeof flags !== 'number') {
// Allow for a single string or an array of string flags
flags = [].concat(flags)
for (i = 0; i < flags.length; i++) {
// Resolve string input to bitwise e.g. 'XDIFF_PATCH_NORMAL' becomes 1
if (OPTS[flags[i]]) {
optTemp = optTemp | OPTS[flags[i]]
}
}
flags = optTemp
}
if (flags & OPTS.XDIFF_PATCH_NORMAL) {
for (i = 0, ll = lines.length; i < ll; i++) {
ranges = lines[i].match(rangeExp)
if (ranges) {
lastLinePos = linePos
linePos = ranges[1] - 1
while (lastLinePos < linePos) {
newStrArr[newStrArr.length] = origLines[lastLinePos++]
}
while (lines[++i] && (rangeExp.exec(lines[i])) === null) {
firstChar = lines[i].charAt(0)
switch (firstChar) {
case '-':
// Skip including that line
++linePos
break
case '+':
newStrArr[newStrArr.length] = lines[i].slice(1)
break
case ' ':
newStrArr[newStrArr.length] = origLines[linePos++]
break
default:
// Reconcile with returning errrors arg?
throw new Error('Unrecognized initial character in unidiff line')
}
}
if (lines[i]) {
i--
}
}
}
while (linePos > 0 && linePos < origLines.length) {
newStrArr[newStrArr.length] = origLines[linePos++]
}
} else if (flags & OPTS.XDIFF_PATCH_REVERSE) {
// Only differs from above by a few lines
for (i = 0, ll = lines.length; i < ll; i++) {
ranges = lines[i].match(rangeExp)
if (ranges) {
lastLinePos = linePos
linePos = ranges[3] - 1
while (lastLinePos < linePos) {
newStrArr[newStrArr.length] = origLines[lastLinePos++]
}
while (lines[++i] && (rangeExp.exec(lines[i])) === null) {
firstChar = lines[i].charAt(0)
switch (firstChar) {
case '-':
newStrArr[newStrArr.length] = lines[i].slice(1)
break
case '+':
// Skip including that line
++linePos
break
case ' ':
newStrArr[newStrArr.length] = origLines[linePos++]
break
default:
// Reconcile with returning errrors arg?
throw new Error('Unrecognized initial character in unidiff line')
}
}
if (lines[i]) {
i--
}
}
}
while (linePos > 0 && linePos < origLines.length) {
newStrArr[newStrArr.length] = origLines[linePos++]
}
}
if (errorObj) {
errorObj.value = errors
}
return newStrArr.join('\n')
}
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How to use

You you can install via npm install locutus and require it via require('locutus/php/xdiff/xdiff_string_patch'). You could also require the xdiff module in full so that you could access xdiff.xdiff_string_patch instead.

If you intend to target the browser, you can then use a module bundler such as Parcel, webpack, Browserify, or rollup.js. This can be important because Locutus allows modern JavaScript in the source files, meaning it may not work in all browsers without a build/transpile step. Locutus does transpile all functions to ES5 before publishing to npm.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.

Notes

  • The XDIFF_PATCH_IGNORESPACE flag and the error argument are not currently supported.

  • This has not been tested exhaustively yet.

  • The errorObj parameter (optional) if used must be passed in as a object. The errors will then be written by reference into it’s value property

Examples

Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#codeexpected result
1xdiff_string_patch('', '@@ -0,0 +1,1 @@\n+Hello world!')'Hello world!'

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