function

util.diff

function diff(
actual: string | readonly string[],
expected: string | readonly string[]
): DiffEntry[];

util.diff() compares two string or array values and returns an array of difference entries. It uses the Myers diff algorithm to compute minimal differences, which is the same algorithm used internally by assertion error messages.

If the values are equal, an empty array is returned.

const { diff } = require('node:util');

// Comparing strings
const actualString = '12345678';
const expectedString = '12!!5!7!';
console.log(diff(actualString, expectedString));
// [
//   [0, '1'],
//   [0, '2'],
//   [1, '3'],
//   [1, '4'],
//   [-1, '!'],
//   [-1, '!'],
//   [0, '5'],
//   [1, '6'],
//   [-1, '!'],
//   [0, '7'],
//   [1, '8'],
//   [-1, '!'],
// ]
// Comparing arrays
const actualArray = ['1', '2', '3'];
const expectedArray = ['1', '3', '4'];
console.log(diff(actualArray, expectedArray));
// [
//   [0, '1'],
//   [1, '2'],
//   [0, '3'],
//   [-1, '4'],
// ]
// Equal values return empty array
console.log(diff('same', 'same'));
// []
@param actual

The first value to compare

@param expected

The second value to compare

@returns

An array of difference entries. Each entry is an array with two elements:

  • Index 0: number Operation code: -1 for delete, 0 for no-op/unchanged, 1 for insert
  • Index 1: string The value associated with the operation

Referenced types

type DiffEntry = [operation: -1 | 0 | 1, value: string]