TheAlgorithms/JavaScript · error · TypeError

Both arguments should be strings.

Error message

Both arguments should be strings.

What it means

Thrown as a TypeError by checkAnagramRegex() when either str1 or str2 is not a string. The function spreads str1 ([...str1]) and compares lengths/characters, all of which assume string inputs. Both arguments must be primitive strings; missing or non-string either one triggers the error.

Source

Thrown at String/CheckAnagram.js:14

// An [Anagram](https://en.wikipedia.org/wiki/Anagram) is a string that is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. Anagram check is not case-sensitive;
/**
 * @function checkAnagramRegex
 * @param {string} str1
 * @param {string} str2
 * @returns {boolean}
 * @description - check anagram with the help of Regex
 * @example - checkAnagramRegex('node', 'deno') => true
 * @example - checkAnagramRegex('Eleven plus two', 'Twelve plus one') => true
 */
const checkAnagramRegex = (str1, str2) => {
  // check that inputs are strings.
  if (typeof str1 !== 'string' || typeof str2 !== 'string') {
    throw new TypeError('Both arguments should be strings.')
  }

  // If both strings have not same lengths then they can not be anagram.
  if (str1.length !== str2.length) {
    return false
  }

  /**
   * str1 converted to an array and traverse each letter of str1 by reduce method
   * reduce method return string which is empty or not.
   */
  return ![...str1].reduce(
    (str2Acc, cur) => str2Acc.replace(new RegExp(cur, 'i'), ''), // remove the similar letter from str2Acc in case-insensitive
    str2
  )
}

/**

View on GitHub (pinned to 5c39e87a9a)

Solutions

1. Default both parameters: checkAnagramRegex(str1 ?? '', str2 ?? '').
2. Guard both: if (typeof a === 'string' && typeof b === 'string').
3. Coerce inputs: checkAnagramRegex(String(a), String(b)).

Example fix

// before
checkAnagramRegex(input1, input2)

// after
checkAnagramRegex(String(input1 ?? ''), String(input2 ?? ''))

function safeCheckAnagramRegex(a, b) {
  if (typeof a !== 'string' || typeof b !== 'string') {
    throw new TypeError('Both arguments must be strings')
  }
  return checkAnagramRegex(a, b)
}

function areBothStrings(a, b) {
  return typeof a === 'string' && typeof b === 'string'
}

try {
  checkAnagramRegex(a, b)
} catch (e) {
  if (e instanceof TypeError && e.message.includes('Both arguments should be strings')) {
    return checkAnagramRegex(String(a ?? ''), String(b ?? ''))
  }
  throw e
}

When it happens

Trigger: Calling checkAnagramRegex(null, 'node'), checkAnagramRegex('node', undefined), checkAnagramRegex(123, '123'), or checkAnagramRegex(['n','o'], 'no'). Only one bad argument is enough since the condition uses OR.

Common situations: Optional function parameters not defaulted; one side coming from JSON that omits a field; comparing a value to itself where the value is undefined.

Related errors

• Invalid Input
• Argument should be string
• Argument is not a string.
• Argument is not a string
• Argument is not a string.

AI-assisted analysis of TheAlgorithms/JavaScript@5c39e87a9a (2026-08-13). Data as JSON: /api/errors/29e176ff87cea150. Report an issue: GitHub.