TheAlgorithms/JavaScript · error · TypeError

the param should be string

Error message

the param should be string

What it means

Guard in maxWord. The function finds the most-occurring word in a sentence and requires sentence to be a string, throwing TypeError otherwise. The parameter defaults to '', so omitting it is safe; only an explicitly non-string value throws.

Source

Thrown at String/MaxWord.js:12

// Given a sentence, return the most occurring word

/**
 * @param {string} sentence - the sentence you want to find the most occurring word
 * @returns {string} - the most occurring word
 *
 * @example
 *     -  maxWord('lala lili lala'); // lala
 */
const maxWord = (sentence = '') => {
  if (typeof sentence !== 'string') {
    throw new TypeError('the param should be string')
  }

  if (!sentence) {
    return null
  }

  const words = sentence.split(' ')
  if (words.length < 2) {
    return words[0]
  }

  const occurrences = {}
  words.forEach((word) => {
    occurrences[word.toLocaleLowerCase()] =
      occurrences[word.toLocaleLowerCase()] + 1 || 1
  })

  const max = Object.keys(occurrences).reduce(

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Coerce null/undefined to '' before calling: sentence ?? ''.
2. Validate typeof at the call site.
3. Join arrays first: arr.join(' ').

Example fix

// before
maxWord(maybeSentence)

// after
maxWord(typeof maybeSentence === 'string' ? maybeSentence : '')

if (typeof sentence !== 'string') {
  throw new TypeError('sentence must be a string')
}
maxWord(sentence)

const isString = (v) => typeof v === 'string'

try {
  maxWord(sentence)
} catch (e) {
  if (e instanceof TypeError) { /* not a string */ } else throw e
}

When it happens

Trigger: Calling maxWord(null), maxWord(42), maxWord(['a','b']), maxWord({}). Any explicit non-string argument. (maxWord() and maxWord(undefined) do NOT throw because the default applies.)

Common situations: A source that returns null on miss instead of undefined (bypassing the default); a number passed where a sentence string was expected; an array passed where a joined string was intended.

Related errors

• The first param should be a string
• The second param should be a boolean
• Argument is not a string.
• Argument is not a string.
• Input should be a string

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/d6c91b54116e60e6. Report an issue: GitHub.