util.diff

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util.diff(actual, expected): Array

Stability: 1Experimental

Attributes

actual:Array | string

The first value to compare

expected:Array | string

The second value to compare

Returns:Array

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

0:number

Operation code: -1 for delete, 0 for no-op/unchanged, 1 for insert

1:string

The value associated with the operation

Algorithm complexity: O(N*D), where:
N is the total length of the two sequences combined (N = actual.length + expected.length)
D is the edit distance (the minimum number of operations required to transform one sequence into the other).

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'));
// []

JavaScript