Regex to extract all matches from a string using RegExp.exec

javascript

regex-engineering

string-manipulation

performance

byAlex Kataev·Mar 4, 2025

To efficiently extract all matches from a string, use RegExp.exec() in a loop with a global regex:

const regex = /pattern/g;  // Insert your regex pattern here
const str = 'text';        // Replace with your string
let matches = [];  // Place to store the magic we're seeking
let match;

while ((match = regex.exec(str))) {  // The magic happens here!
  matches.push(match[0]);  // Presto! Here's your match
}

// For capturing groups — the rabbit in the hat trick — you can use match[1], match[2], etc.

The matches array will now hold all occurrences of your pattern in the str.

Key and value extraction unpacked

When you need to extract key-value pairs with a special format, a regex like \s*([^:]+):"([^"]+)", alongside the global (g) and multiline (m) flags, will do the trick:

const keyValueRegex = /\s*([^:]+):"([^"]+)"/gm;  // The regex scope widens
const keyValueString = 'key1:"value1" key2:"value2"'  // Our hunting ground
let keyValueMatch;
let keyValuePairs = {};

while ((keyValueMatch = keyValueRegex.exec(keyValueString)) !== null) { // Watch the magic unfold
  let key = keyValueMatch[1];  // Abracadabra! The key appears
  let value = keyValueMatch[2];  // Alakazam! And here's the value
  keyValuePairs[key] = value;  // Key and value, a match made in heaven
}

Alternate methods for a different show

For different tricks under your sleeves, string.matchAll() can be used for a simplified iteration over matches:

const matches = [...keyValueString.matchAll(keyValueRegex)]; // The cloaked magician reveals it all
for (const match of matches) {
  console.log(`Key: ${match[1]}, Value: ${match[2]}`);
}

Or, introduce replace() for an elegant performance without the need to store matches:

keyValueString.replace(keyValueRegex, (fullMatch, key, value) => {
  console.log(`Key: ${key}, Value: ${value}`); // Poof! And they're gone, after the show
});

Craft like a master regex-smith

Develop efficient patterns to ensure your performance doesn't vanish into thin air.
Always escape special characters that aren't just smoke and mirrors, like \. or \\ in JavaScript regex patterns.
Test your regular expressions with a variety of input to ensure they can handle whatever subroutine the audience throws at it.

The importance of knowing your act

Understand the structure of your input for an accurate performance. If your keys are finite to word characters, your regex may look like this (\w+):"([^"]+)".

Handling complex crowds

For nested or complex text structures, keep an ace in your pocket with recursive functions or additional logic within your loop to deal with your sub-patterns or special cards.

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