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. 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.
  • 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.