Arranging words by their length in a sentence in JavaScript

In JavaScript, you can arrange words in a sentence by their length using string manipulation and array sorting methods. This technique is useful for text processing and formatting applications.

A sentence is a string of characters joined by whitespaces. The goal is to rearrange words so the shortest word appears first, followed by progressively longer ones.

Problem Example

If the input string is:

const str = 'this is a string';

Then the output should be:

const output = 'a is this string';

Solution Using Array Methods

Here's a complete solution that sorts words by length while preserving original order for words of equal length:

const str = 'this is a string';

const arrangeWords = (str = '') => {
    const data = str.toLowerCase().split(' ').map((val, i) => {
        return {
            str: val,
            length: val.length,
            index: i
        }
    });
    
    data.sort((a, b) => {
        if (a.length === b.length)
            return (a.index - b.index);
        return (a.length - b.length);
    });
    
    let res = '';
    let i = 0;
    while (i < data.length - 1)
        res += (data[i++].str + ' ');
    res += data[i].str;
    
    return res;
};

console.log(arrangeWords(str));

a is this string

How It Works

The solution works in several steps:

1. Convert to lowercase: Ensures consistent comparison
2. Split into words: Creates an array of individual words
3. Map with metadata: Creates objects containing the word, its length, and original index
4. Sort by length: Primary sort by length, secondary sort by original position
5. Reconstruct string: Joins the sorted words back into a sentence

Alternative Simplified Approach

For a more concise solution without preserving original order for equal-length words:

const arrangeWordsByLength = (sentence) => {
    return sentence.toLowerCase()
        .split(' ')
        .sort((a, b) => a.length - b.length)
        .join(' ');
};

const str = 'this is a string';
console.log(arrangeWordsByLength(str));

a is this string

Comparison of Methods

Conclusion

Use the object-based approach when you need to preserve the original order of equal-length words. For simpler cases, the direct sorting method provides cleaner code with the same core functionality.