A javascript text differencing implementation.

Based on the algorithm proposed in "An O(ND) Difference Algorithm and its Variations" (Myers, 1986).

npm install diff --save

• Diff.diffChars(oldStr, newStr[, options]) - diffs two blocks of text, comparing character by character.

  Returns a list of change objects (See below).

  Options

  • ignoreCase: true to ignore casing difference. Defaults to false.

• Diff.diffWords(oldStr, newStr[, options]) - diffs two blocks of text, comparing word by word, ignoring whitespace.

  Returns a list of change objects (See below).

  Options

  • ignoreCase: Same as in diffChars.

• Diff.diffWordsWithSpace(oldStr, newStr[, options]) - diffs two blocks of text, comparing word by word, treating whitespace as significant.

  Returns a list of change objects (See below).

• Diff.diffLines(oldStr, newStr[, options]) - diffs two blocks of text, comparing line by line.

  Options

  • ignoreWhitespace: true to ignore leading and trailing whitespace. This is the same as diffTrimmedLines
  • newlineIsToken: true to treat newline characters as separate tokens. This allows for changes to the newline structure to occur independently of the line content and to be treated as such. In general this is the more human friendly form of diffLines and diffLines is better suited for patches and other computer friendly output.

  Returns a list of change objects (See below).

• Diff.diffTrimmedLines(oldStr, newStr[, options]) - diffs two blocks of text, comparing line by line, ignoring leading and trailing whitespace.

  Returns a list of change objects (See below).

• Diff.diffSentences(oldStr, newStr[, options]) - diffs two blocks of text, comparing sentence by sentence.

  Returns a list of change objects (See below).

• Diff.diffCss(oldStr, newStr[, options]) - diffs two blocks of text, comparing CSS tokens.

  Returns a list of change objects (See below).

• Diff.diffJson(oldObj, newObj[, options]) - diffs two JSON objects, comparing the fields defined on each. The order of fields, etc does not matter in this comparison.

  Returns a list of change objects (See below).

• Diff.diffArrays(oldArr, newArr[, options]) - diffs two arrays, comparing each item for strict equality (===).

  Options

  • comparator: function(left, right) for custom equality checks

  Returns a list of change objects (See below).

• Diff.createTwoFilesPatch(oldFileName, newFileName, oldStr, newStr, oldHeader, newHeader) - creates a unified diff patch.

  Parameters:

  • oldFileName : String to be output in the filename section of the patch for the removals
  • newFileName : String to be output in the filename section of the patch for the additions
  • oldStr : Original string value
  • newStr : New string value
  • oldHeader : Additional information to include in the old file header
  • newHeader : Additional information to include in the new file header
  • options : An object with options.
    • context describes how many lines of context should be included.
    • ignoreWhitespace: true to ignore leading and trailing whitespace.
    • newlineIsToken: true to treat newline characters as separate tokens. This allows for changes to the newline structure to occur independently of the line content and to be treated as such. In general this is the more human friendly form of diffLines and diffLines is better suited for patches and other computer friendly output.

• Diff.createPatch(fileName, oldStr, newStr, oldHeader, newHeader) - creates a unified diff patch.

  Just like Diff.createTwoFilesPatch, but with oldFileName being equal to newFileName.

• Diff.structuredPatch(oldFileName, newFileName, oldStr, newStr, oldHeader, newHeader, options) - returns an object with an array of hunk objects.

  This method is similar to createTwoFilesPatch, but returns a data structure suitable for further processing. Parameters are the same as createTwoFilesPatch. The data structure returned may look like this:

  {
    oldFileName: 'oldfile', newFileName: 'newfile',
    oldHeader: 'header1', newHeader: 'header2',
    hunks: [{
      oldStart: 1, oldLines: 3, newStart: 1, newLines: 3,
      lines: [' line2', ' line3', '-line4', '+line5', '\\ No newline at end of file'],
    }]
  }

• Diff.applyPatch(source, patch[, options]) - applies a unified diff patch.

  Return a string containing new version of provided data. patch may be a string diff or the output from the parsePatch or structuredPatch methods.

  The optional options object may have the following keys:

  • fuzzFactor: Number of lines that are allowed to differ before rejecting a patch. Defaults to 0.
  • compareLine(lineNumber, line, operation, patchContent): Callback used to compare to given lines to determine if they should be considered equal when patching. Defaults to strict equality but may be overridden to provide fuzzier comparison. Should return false if the lines should be rejected.

• Diff.applyPatches(patch, options) - applies one or more patches.

  This method will iterate over the contents of the patch and apply to data provided through callbacks. The general flow for each patch index is:

  • options.loadFile(index, callback) is called. The caller should then load the contents of the file and then pass that to the callback(err, data) callback. Passing an err will terminate further patch execution.
  • options.patched(index, content, callback) is called once the patch has been applied. content will be the return value from applyPatch. When it's ready, the caller should call callback(err) callback. Passing an err will terminate further patch execution.

  Once all patches have been applied or an error occurs, the options.complete(err) callback is made.

• Diff.parsePatch(diffStr) - Parses a patch into structured data

  Return a JSON object representation of the a patch, suitable for use with the applyPatch method. This parses to the same structure returned by Diff.structuredPatch.

• convertChangesToXML(changes) - converts a list of changes to a serialized XML format

All methods above which accept the optional callback method will run in sync mode when that parameter is omitted and in async mode when supplied. This allows for larger diffs without blocking the event loop. This may be passed either directly as the final parameter or as the callback field in the options object.

Many of the methods above return change objects. These objects consist of the following fields:

• value: Text content
• added: True if the value was inserted into the new string
• removed: True if the value was removed from the old string

Note that some cases may omit a particular flag field. Comparison on the flag fields should always be done in a truthy or falsy manner.

Basic example in Node

require('colors');
const Diff = require('diff');

const one = 'beep boop';
const other = 'beep boob blah';

const diff = Diff.diffChars(one, other);

diff.forEach((part) => {
  // green for additions, red for deletions
  // grey for common parts
  const color = part.added ? 'green' :
    part.removed ? 'red' : 'grey';
  process.stderr.write(part.value[color]);
});

console.log();

Running the above program should yield

Basic example in a web page

<pre id="display"></pre>
<script src="diff.js"></script>
<script>
const one = 'beep boop',
    other = 'beep boob blah',
    color = '';
    
let span = null;

const diff = Diff.diffChars(one, other),
    display = document.getElementById('display'),
    fragment = document.createDocumentFragment();

diff.forEach((part) => {
  // green for additions, red for deletions
  // grey for common parts
  const color = part.added ? 'green' :
    part.removed ? 'red' : 'grey';
  span = document.createElement('span');
  span.style.color = color;
  span.appendChild(document
    .createTextNode(part.value));
  fragment.appendChild(span);
});

display.appendChild(fragment);
</script>

Open the above .html file in a browser and you should see

Full online demo

jsdiff supports all ES3 environments with some known issues on IE8 and below. Under these browsers some diff algorithms such as word diff and others may fail due to lack of support for capturing groups in the split operation.

See LICENSE.