How to put variable in regular expression match with JavaScript?

You can put a variable in a regular expression match by using the RegExp constructor, which accepts variables as patterns. This is essential when you need dynamic pattern matching in JavaScript.

Syntax

// Using RegExp constructor with variable
let pattern = new RegExp(variableName, flags);
string.match(pattern);

// Or directly with match()
string.match(variableName); // for simple string matching

Example: Using Variable in Regular Expression

let sentence = 'My Name is John';
console.log("The actual value:");
console.log(sentence);

let matchWord = 'John';
console.log("The matching value:");
console.log(matchWord);

// Using RegExp constructor with variable
let matchRegularExpression = new RegExp(matchWord, 'g');
let result = sentence.match(matchRegularExpression);
console.log("Match result:");
console.log(result);

The actual value:
My Name is John
The matching value:
John
Match result:
[ 'John' ]

Using Different Flags

let text = 'JavaScript is great. I love JavaScript!';
let searchTerm = 'javascript';

// Case-insensitive search using 'i' flag
let caseInsensitive = new RegExp(searchTerm, 'gi');
console.log("Case-insensitive match:");
console.log(text.match(caseInsensitive));

// Global search for exact case
let exactCase = new RegExp('JavaScript', 'g');
console.log("Exact case matches:");
console.log(text.match(exactCase));

Case-insensitive match:
[ 'JavaScript', 'JavaScript' ]
Exact case matches:
[ 'JavaScript', 'JavaScript' ]

Special Characters in Variables

let textWithSpecialChars = 'Price: $25.99 and $15.50';
let dollarPattern = '\$\d+\.\d+';

// Using variable with escaped special characters
let priceRegex = new RegExp(dollarPattern, 'g');
let prices = textWithSpecialChars.match(priceRegex);
console.log("Found prices:");
console.log(prices);

Found prices:
[ '$25.99', '$15.50' ]

Comparison of Methods

Conclusion

Use new RegExp(variable, flags) when you need dynamic pattern matching with variables. This approach provides flexibility for runtime pattern creation and supports all regex flags.