tessl/npm-jest-diff

Display differences clearly so people can review changes confidently

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Overview

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Files

String Comparison

Name: tessl/npm-jest-diff
Author: tessl

Character-by-character string comparison with unified diff output, semantic cleanup, and support for both single-line and multi-line strings.

Capabilities

Unified String Diff

Compares two strings character-by-character and returns formatted unified diff output.

/**
 * Compare two strings character-by-character and format as comparison lines
 * in which changed substrings have inverse colors
 * @param a - First string to compare
 * @param b - Second string to compare
 * @param options - Optional formatting configuration
 * @returns Formatted unified diff string
 */
function diffStringsUnified(a: string, b: string, options?: DiffOptions): string;

Features:

Multiline Detection: Automatically detects multiline strings and appends newlines for proper alignment
Character-level Highlighting: Shows exact character differences with color highlighting
Common Substring Detection: Identifies and preserves common substrings for readability
Fallback Handling: Falls back to line-by-line diff when character diff isn't meaningful

Usage Examples:

import { diffStringsUnified } from "jest-diff";

// Single-line strings
const result1 = diffStringsUnified("Hello world", "Hello Jest");
console.log(result1);

// Multi-line strings
const text1 = `Line 1
Line 2
Line 3`;
const text2 = `Line 1
Modified Line 2
Line 3`;
const result2 = diffStringsUnified(text1, text2);
console.log(result2);

// With custom options
const result3 = diffStringsUnified("old text", "new text", {
  aAnnotation: "Original",
  bAnnotation: "Updated", 
  contextLines: 2
});
console.log(result3);

Raw String Diff

Compares two strings character-by-character and returns raw diff operations array.

/**
 * Compare two strings character-by-character and return raw diff operations
 * @param a - First string to compare
 * @param b - Second string to compare
 * @param cleanup - Whether to apply semantic cleanup to improve diff quality
 * @returns Array of Diff objects representing the operations
 */
function diffStringsRaw(a: string, b: string, cleanup: boolean): Array<Diff>;

Cleanup Process:

Semantic Cleanup: When enabled, eliminates semantically trivial equalities and improves diff readability
Overlap Detection: Finds overlaps between deletions and insertions to reduce noise
Boundary Alignment: Aligns edits to word and line boundaries where possible

Usage Examples:

import { diffStringsRaw, DIFF_DELETE, DIFF_INSERT, DIFF_EQUAL } from "jest-diff";

// Basic usage with cleanup
const diffs = diffStringsRaw("Hello world", "Hello Jest", true);
diffs.forEach(diff => {
  const [op, text] = [diff[0], diff[1]];
  switch (op) {
    case DIFF_DELETE:
      console.log(`Delete: "${text}"`);
      break;
    case DIFF_INSERT:
      console.log(`Insert: "${text}"`);
      break;
    case DIFF_EQUAL:
      console.log(`Keep: "${text}"`);
      break;
  }
});

// Without cleanup for raw operations
const rawDiffs = diffStringsRaw("abc", "axc", false);
console.log(rawDiffs);

Diff Operations

class Diff {
  0: number; // Operation type
  1: string; // Text content
  constructor(op: number, text: string);
}

const DIFF_DELETE = -1; // Text was deleted from first string
const DIFF_INSERT = 1;  // Text was inserted in second string  
const DIFF_EQUAL = 0;   // Text is common to both strings