JavaScript: Find the most frequent word in a string

Last update on July 17 2025 12:57:01 (UTC/GMT +8 hours)

JavaScript String: Exercise-59 with Solution

Most Frequent Word

Write a JavaScript program to find the most frequent word in a given string.
Test Data:
("The quick brown fox jumps over the lazy dog") -> "the"
("Python is a high-level, general-purpose programming language.") -> "python"
(" It was the same man, she was sure of it. It's always the same, Chauncey.") -> "was"
(12321) -> "It must be a string."

Sample Solution:

JavaScript Code:

// Define a function named 'test' with a single parameter 'text'
const test = (text) => { 
   // Check if the input string is empty
   if (text.length === 0) 
    {
    // Return a message if the input string is empty
    return 'String should not be empty!'
   }
    // Check if the input parameter 'text' is not a string
    if (typeof text !== 'string')
     {
       // Return a message if the input is not a string
       return 'It must be a string.'
     }
   // Split the input text into an array of words using space as the delimiter
   const data = text.split(' ')
  // If there's only one word in the text, return that word
  if (data.length < 2) {
    return data[0]
  }
   // Split the input text into an array of words using space as the delimiter
   const words = text.split(' ')
  // If there's only one word in the text, return that word
  if (words.length < 2) {
    return words[0]
  }
  // Create an empty object to store word frequencies
  const temp = {}
  // Iterate through each word in the array of words
  words.forEach(word => {
    // Convert each word to lowercase and increment its frequency in the 'temp' object
    temp[word.toLocaleLowerCase()] = temp[word.toLocaleLowerCase()] + 1 || 1
  })
  // Find the word with the maximum frequency in the 'temp' object
  const max = Object.keys(temp).reduce((n, word) => {
    // If the frequency of the current word is greater than the maximum frequency seen so far, update 'max'
    if (temp[word] > n.count) 
    { 
      return { word, count: temp[word] } 
    } 
    else 
    { 
      return n 
    }
  }, { word: '', count: 0 })
  // Return the word with the maximum frequency
  return max.word
}
// Test the 'test' function with different input strings and output the result
console.log(test("The quick brown fox jumps over the lazy dog"))  // 'the'
console.log(test("Python is a high-level, general-purpose programming language."))  // 'a'
console.log(test(" It was the same man, she was sure of it. It's always the same, Chauncey."))  // 'the'
console.log(test(12321))  // It must be a string.

Output:

the
python
was
It must be a string.

Explanation:

In the exercise above,

The function "test()" is defined using arrow function syntax, taking a single parameter named 'text'.
It first checks if the input string is empty. If it is, the function returns a message indicating that the string should not be empty.
Next, it checks if the input parameter 'text' is not a string using the 'typeof' operator. If it's not a string, the function returns a message indicating it must be a string.
If the input is a non-empty string, the function splits the text into an array of words using space as the delimiter.
If there's only one word in the text, the function returns that word.
It then creates an empty object to store word frequencies and iterates through each word in the array of words.
For each word, it converts it to lowercase and increments its frequency in the object.
After counting the frequencies of each word, the function finds the word with the maximum frequency by iterating through the object's entries.

Flowchart:

Live Demo:

See the Pen javascript-string-exercise-59 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

Write a JavaScript function that splits a string into words and finds the most frequently occurring word using a frequency counter.
Write a JavaScript function that converts the string to lowercase before counting word occurrences for case-insensitivity.
Write a JavaScript function that handles punctuation by stripping non-alphanumeric characters prior to word counting.
Write a JavaScript function that returns a message indicating the most frequent word and its count.

Go to:

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