finding the word at a position in javascript

javascript, string

Solution

function getWordAt (str, pos) {
    // check ranges
    if ((pos < 0) || (pos > str.length)) {
        return '';
    }
    // Perform type conversions.
    str = String(str);
    pos = Number(pos) >>> 0;
    
    // Search for the word's beginning and end.
    var left = str.slice(0, pos + 1).search(/\S+$/), // use /\S+\s*$/ to return the preceding word 
        right = str.slice(pos).search(/\s/);
    
    // The last word in the string is a special case.
    if (right < 0) {
        return str.slice(left);
    }
    
    // Return the word, using the located bounds to extract it from the string.
    return str.slice(left, right + pos);
    
}

This function accepts any whitespace character as a word separator, including spaces, tabs, and newlines. Essentially, it looks:

- For the beginning of the word, matched by `/\S+$/`

- Just past the end of the word, using `/\s/`

As written, the function will return `""` if the index of a whitespace character is given; spaces are not part of words themselves. If you want the function to instead return the preceding word, change `/\S+$/` to `/\S+\s*$/`.

Here is some example output for `"This is a sentence."`

0: This
1: This
2: This
3: This
4:
5: is
6: is
7:
8: a
9:
10: sentence.
// ...
18: sentence.

Modified to return the preceding word, the output becomes:

0: This
1: This
2: This
3: This
4: This
5: is
6: is
7: is
8: a
9: a
10: sentence.
// ...
18: sentence.

Problem

For string input of 'this is a sentence' it must return 'is' when position is 6 or 7. When position is 0, 1, 2, 3 or 4 result must be 'this'. What is the easiest way?

Original source