Ekene Agunechemba



👋 Hey there, young coder!

Today, you’re going to learn how to search for things in a string using something cool in JavaScript called .exec(). Think of it like using a magnifying glass to find hidden patterns or letters in a sentence.

Let’s jump in! 🚀

🧠 What is .exec()?

.exec() is a tool in JavaScript that helps you search for matches in a word or sentence using something called a regular expression (also called regex).

Here’s a simple example:

var re = /([0-9]+)[a-z]+/;
var match = re.exec("foo123bar");

This means:

  • The pattern says: “Find one or more numbers, then one or more letters”
  • The string is "foo123bar"

💡 Here’s what happens:

  • match[0] → "123bar" (the full thing it matched)
  • match[1] → "123" (only the number part)
  • match.index → 3 (where the match starts)

🎯 Visual Example:

String:   f  o  o  1  2  3  b  a  r
Index:    0  1  2  3  4  5  6  7  8
Match:          1  2  3  b  a  r
               ^ match starts here (index 3)

🔁 Loop Through Matches with .exec()

What if we want to find all the times a letter appears? Let’s use a loop!

var re = /a/g;
var result;

while ((result = re.exec('barbatbaz')) !== null) {
  console.log("found '" + result[0] + "', next exec starts at index '" + re.lastIndex + "'");
}

👀 What’s happening here?

  • /a/g → “Find all ‘a’s” (g means global)
  • .exec() finds one “a” at a time
  • The loop keeps going until no more “a”s are found
  • re.lastIndex tells where the search will start next

🖨 Output:

found 'a', next exec starts at index '2'
found 'a', next exec starts at index '5'
found 'a', next exec starts at index '8'

🍎 Think of it like a Treasure Hunt!

You’re searching a word for every letter “a”. Each time you find one, you shout:

“Hey! Found one at spot X! Let’s look for the next one!”

And the hunt goes on until all are found!

🧪 Review Time! Try These Practice Questions

  1. What does .exec() do in JavaScript? A) It makes a loop B) It searches for matches in a string C) It adds numbers D) It styles text

  2. What will match[1] give you? A) The full sentence B) The starting index C) The captured part of the match D) The number of matches

  3. What does the g flag in /a/g mean? A) Get one B) Go back C) Global – find all matches D) Great match

  4. If .exec() doesn’t find anything, what does it return? A) 0 B) “Nope” C) null D) undefined

  5. In the word "abcabc", how many times will /a/g.exec() find a match?

🧠 Tip: You can try out all these in your browser’s developer console!

<
Previous Post
🧠 Python Lesson: Built-in Math Functions and Utility Modules
>
Next Post
JS REGEX 06: JavaScript Matching Tools .exec() vs .test() vs .match()