`diffWords` produces duplicate spaces with `oneChangePerToken`
Author: aforemendudeCreated Aug 12, 2026Updated Aug 12, 2026
When diffWords is called with oneChangePerToken set to true, the output contains duplicate spaces. The other text diff methods don't output duplicate separators.
Reproduced on the latest v9.0.0. Happening to the latest master as well.
Reproduction:
https://github.com/aforemendude/bugs-reproduction/tree/main/jsdiff-one-change-per-token
import {
diffChars,
diffLines,
diffSentences,
diffWords,
diffWordsWithSpace,
} from 'diff'
const options = { oneChangePerToken: true }
const diffCases = [
['diffChars', diffChars, 'cat dog', 'cat dig'],
['diffWords', diffWords, 'a b', 'a c'],
['diffWordsWithSpace', diffWordsWithSpace, 'red blue', 'red green'],
['diffLines', diffLines, 'red\nblue\n', 'red\ngreen\n'],
[
'diffSentences',
diffSentences,
'The cat sleeps. The dog runs.',
'The cat rests. The dog runs.',
],
]
for (const [name, diffMethod, oldText, newText] of diffCases) {
const changes = diffMethod(oldText, newText, options)
console.log(`${name} (${JSON.stringify(oldText)} -> ${JSON.stringify(newText)}):`)
console.log('changes:', JSON.stringify(changes, null, 2))
console.log('------------------------------')
}diffWords outputs a (a + space), b (space + b), and c (space + c). The input only has 1 space, but the output has 2 (after a, and before b/c).
diffWords ("a b" -> "a c"):
changes: [
{
"count": 1,
"added": false,
"removed": false,
"value": "a "
},
{
"count": 1,
"added": false,
"removed": true,
"value": " b"
},
{
"count": 1,
"added": true,
"removed": false,
"value": " c"
}
]All other text diff methods (diffChars, diffLines, diffSentences, diffWordsWithSpace) are working properly.
Source: kpdecker/jsdiff