myers-diff

A JavaScript test differentiation implementation based on An O(ND) Difference Algorithm and Its Variations (1986). It is a lightweight, low-level, no-frills library that can be used to build bulkier viewers.

Installation

$ npm install myers-diff

Getting started

With basic usage:

const myers = require('myers-diff');

const lhs = 'the quick red fox jumped\nover the hairy dog';
const rhs = 'the quick brown fox jumped\nover the lazy dog';

const diff = myers.diff(lhs, rhs);

console.log(myers.formats.GnuNormalFormat(diff));
console.log(diff);
//
// 1,2c1,2
// < the quick red fox jumped
// < over the hairy dog
// ---
// > the quick brown fox jumped
// > over the lazy dog

With all options:

const myers = require('myers-diff');

const lhs = 'the quick red fox jumped\nover the hairy dog';
const rhs = 'the quick brown fox jumped\nover the lazy dog';

const diff = myers.diff(lhs, rhs, {
    compare: 'lines',
    ignoreWhitespace: false,
    ignoreCase: false,
    ignoreAccents: false
});

For building visual editors:

const { diff, changed } = require('myers-diff');
const lhs = 'the quick red fox jumped\nover the hairy dog';
const rhs = 'the quick brown fox jumped\nover the lazy dog';
const changes = diff(lhs, rhs);

for (const change of changes) {
    if (changed(change.lhs)) {
        // deleted
        const { pos, text, del, length } = change.lhs;
    }
    if (changed(change.rhs)) {
        // added
        const { pos, text, add, length } = change.rhs;
    }
}

API

• myers
  • myers.diff(lhs, rhs, [options])
  • myers.formats
    • GnuNormalFormat
  • myers.changed(part)
• Types
  • Change
  • LeftPart
  • RightPart

myers.diff(lhs, rhs, [options])

Compare lhs text to rhs text. lhs and rhs can also be an arbitrary array if compare is set to 'chars'. Changes are compared from left to right such that items are deleted from left or added to right.

• lhs <string> - The left-hand side text to compare.
• rhs <string> - The right-hand side text to compare.
• options <object> - Diff options.
  • compare <string> - Comparison mode ('lines', 'words', 'chars').
  • ignoreWhitespace <boolean> - Ignores whitespace characters.
  • ignoreCase <boolean> - Ignores whitespace characters.
  • ignoreAccents <boolean> - Ignores accent characters.
• Returns: <Change[]> - Returns an array of Change.

Change

An object that describes a change occurrence between the left-hand text and right-hand text.

• lhs <LeftPart>- Describes the left-hand change.
• rhs <RightPart> - Describes the right-hand change.

LeftPart

Describes a left-hand change occurrence.

• at <number> - The part item identifier. When comparing lines, it is the n-th line; when comparing words, it is the n-th word; when comparing chars, it is the n-th char.
• del <number> - The number of parts deleted from the left. When comparing lines, it is the number of lines deleted; when comparing words, it is the number of words deleted; when comparing chars, it is the number of chars deleted.
• pos <number> - The zero-based character position of the part from the original text.
• text <string> - The text that was changed.
• length <number> - The number of characters.

RightPart

Describes a right-hand change occurrence.

• at <number> - The part item identifier. When comparing lines, it is the n-th line; when comparing words, it is the n-th word; when comparing chars, it is the n-th char.
• add <number> - The number of parts added from the right. When comparing lines, it is the number of lines added; when comparing words, it is the number of words added; when comparing chars, it is the number of chars added.
• pos <number> - The zero-based character position of the part from the original text.
• text <string> - The text that was changed.
• length <number> - The number of characters.

myers.formats

Formatting functions.

GnuNormalFormat(changes)

Formats an array of Change in GNU Normal Format.

• changes <Change[]> - An array of changes from myers.diff.
• Returns <string> The diff text.

myers.changed(part)

Examines the LeftPart or RightPart part to determine if was changed. It is possible for a Change to only affect one side or the other, or both. If changed, it returns true, otherwise, it returns false.

• part <LeftPart | RightPart>- The left-hand part or right-hand part to compare.
• Returns: <boolean> Returns true if changed, otherwise, it returns false.