Find number of replacements when using a global Regular Expression

Question

I have a sentence (string) containing words. I want to replace all occurrences of a word with another. I use newString = oldString.replace(/w1/gi, w2);, but now I need to report to the user how many words I actually replaced.

Is there a quick way to do it without resorting to:

Replacing one word at a time and counting.
Comparing oldString to newString word-by-word and tallying the differences? (The easy case is if oldString === newString => 0 replacements, but beyond that, I'll have to run over both and compare).

Is there any RegEx "trickery" I can use here, or should I just avoid using the g flag?

Use a callback var cnt=0; var res = s.replace(/str/g, function($0) { cnt++; return 'newstr';}); — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 5, 2017 at 17:09

KevBot · Accepted Answer · 2017-07-05 17:35:23Z

3

Option 1: Using the `replace` callback

By using the callback, you can increment a counter, and then return the new word in the callback, this allows you to traverse the string only 1 time, and achieve a count.

var string = 'Hello, hello, hello, this is so awesome';
var count = 0;
string = string.replace(/hello/gi, function() {
  count++;
  return 'hi';
});

console.log('New string:', string);
console.log('Words replaced', count);

Option 2: Using `split` and `join`

Also using the split method, instead of using regex, just join with the new word to create the new string. This solution allows you to avoid using regex at all to achieve counts.

var string = 'Hello, hello, hello, this is so awesome';

string = string.split(/hello/i);
var count = string.length - 1;
string = string.join('Hi');

console.log('New string:', string);
console.log('Words replaced', count);

answered Jul 5, 2017 at 17:35

KevBot

19k5 gold badges54 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Traveling Tech Guy Over a year ago

Yes! The replace function parameter was what I needed! Thanks!

Jeremy Jackson · Accepted Answer · 2017-07-05 16:05:45Z

2

You could split the string with the regex you're using and get the length.

oldString.split(/w1/gi).length - 1

Working example:

var string = "The is the of the and the";
var newString = string.replace(/the/gi, "hello");

var wordsReplaced = string.split(/the/gi).length - 1;

console.log("Words replaced: ", wordsReplaced);

answered Jul 5, 2017 at 16:05

Jeremy Jackson

2,25718 silver badges24 bronze badges

1 Comment

Traveling Tech Guy Over a year ago

Thanks for this - it would work! I'm hoping there's a more efficient way then re-traversing the original string though. If we can't find one - your answer will serve.

Collectives™ on Stack Overflow

Find number of replacements when using a global Regular Expression

2 Answers 2

Option 1: Using the `replace` callback

Option 2: Using `split` and `join`

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Option 1: Using the replace callback

Option 2: Using split and join

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related

Option 1: Using the `replace` callback

Option 2: Using `split` and `join`