tessl/npm-diff

A JavaScript text diff implementation based on the Myers algorithm for comparing text at different granularities.

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Overview

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Files

Character Diffing

Name: tessl/npm-diff
Author: tessl

Character-by-character text comparison with Unicode support and case-insensitive options. Treats each Unicode code point as a separate token for fine-grained text analysis.

Capabilities

diffChars Function

Performs character-level diff between two strings, treating each character as a token.

/**
 * Compare two strings at the character level
 * @param oldStr - Original string
 * @param newStr - New string to compare against
 * @param options - Configuration options
 * @returns Array of change objects representing the diff
 */
function diffChars(oldStr, newStr, options);

Options:

interface CharDiffOptions extends DiffOptions {
  ignoreCase?: boolean;  // Treat uppercase and lowercase as equal
}

Usage Examples:

import { diffChars } from "diff";

// Basic character diff
const result = diffChars("abc", "axc");
console.log(result);
// [
//   { value: "a", count: 1 },
//   { value: "b", removed: true, count: 1 },
//   { value: "x", added: true, count: 1 },
//   { value: "c", count: 1 }
// ]

// Case-insensitive comparison
const caseResult = diffChars("Hello", "HELLO", { ignoreCase: true });
console.log(caseResult);
// [{ value: "Hello", count: 5 }]  // No changes detected

// Unicode support
const unicodeResult = diffChars("café", "cafe");
// Properly handles accented characters as separate tokens

Visual Diff Rendering:

import { diffChars } from "diff";

function renderDiff(oldStr, newStr) {
  const diff = diffChars(oldStr, newStr);
  
  diff.forEach((part) => {
    const color = part.added ? 'green' : 
                  part.removed ? 'red' : 'grey';
    process.stderr.write(part.value[color]);
  });
}

renderDiff("beep boop", "beep boob blah");

characterDiff Instance

Pre-configured Diff instance for character-level comparisons.

/**
 * Pre-configured character diff instance
 * Can be used directly or extended for custom behavior
 */
const characterDiff: Diff;

Usage Examples:

import { characterDiff } from "diff";

// Direct usage
const result = characterDiff.diff("old", "new");

// Custom async usage
characterDiff.diff("old", "new", (result) => {
  console.log("Async result:", result);
});

Advanced Usage

Async Character Diffing

For large strings, use async mode to prevent blocking:

import { diffChars } from "diff";

// Using callback for async operation
diffChars(largeOldString, largeNewString, (result) => {
  console.log("Diff completed:", result);
});

// Or with options
diffChars(largeOldString, largeNewString, {
  ignoreCase: true,
  callback: (result) => {
    console.log("Case-insensitive async diff:", result);
  }
});

Performance Considerations

import { diffChars } from "diff";

// Limit computation for very different strings
const result = diffChars(str1, str2, {
  maxEditLength: 1000,  // Stop if edit distance exceeds 1000
  timeout: 5000         // Timeout after 5 seconds
});

if (!result) {
  console.log("Diff computation exceeded limits");
}

Granular Change Objects

import { diffChars } from "diff";

// Get one change object per character
const granular = diffChars("abc", "axc", {
  oneChangePerToken: true
});

// Results in separate change objects for each character
// instead of combining consecutive changes

Install with Tessl CLI