JavaScript RegExp Objects

RegExp Object Properties

regex.source

regex.flags

regex.global

regex.lastIndex

🔹 Creating RegExp Objects

Two ways to create RegExp objects:

// Method 1: Literal notation
let regex1 = /pattern/flags;

// Method 2: Constructor
let regex2 = new RegExp("pattern", "flags");

// Examples
let emailRegex = /\w+@\w+\.\w+/gi;
let phoneRegex = new RegExp("\\d{3}-\\d{3}-\\d{4}", "g");

console.log("Email regex:", emailRegex);
console.log("Phone regex:", phoneRegex);
console.log("Are they equal?", emailRegex === phoneRegex);

🔹 RegExp Properties in Action

Exploring RegExp object properties:

// Create a RegExp with various flags
let regex = /hello/gim;

console.log("Pattern source:", regex.source);
console.log("All flags:", regex.flags);
console.log("Global flag:", regex.global);
console.log("IgnoreCase flag:", regex.ignoreCase);
console.log("Multiline flag:", regex.multiline);
console.log("Unicode flag:", regex.unicode);
console.log("Sticky flag:", regex.sticky);
console.log("DotAll flag:", regex.dotAll);

🔹 lastIndex Property

The lastIndex property tracks position in global searches:

// Global regex remembers position
let regex = /\d+/g;
let text = "I have 5 cats and 3 dogs";

console.log("Initial lastIndex:", regex.lastIndex);

let match1 = regex.exec(text);
console.log("First match:", match1[0], "at index", match1.index);
console.log("lastIndex after first match:", regex.lastIndex);

let match2 = regex.exec(text);
console.log("Second match:", match2[0], "at index", match2.index);
console.log("lastIndex after second match:", regex.lastIndex);

let match3 = regex.exec(text);
console.log("Third match:", match3);

🔹 Dynamic RegExp Creation

Creating RegExp objects dynamically with variables:

// Dynamic pattern creation
function createSearchRegex(searchTerm, caseSensitive = false) {
    // Escape special characters
    let escapedTerm = searchTerm.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
    let flags = caseSensitive ? 'g' : 'gi';
    return new RegExp(escapedTerm, flags);
}

// Test with different search terms
let searches = ["hello", "[email protected]", "price: $19.99"];
let text = "Hello world! Contact [email protected] for price: $19.99";

searches.forEach(term => {
    let regex = createSearchRegex(term);
    let matches = text.match(regex);
    console.log(`Searching for "${term}":`, matches);
});

🔹 RegExp Object Comparison

Comparing RegExp objects and their properties:

// RegExp objects are compared by reference, not content
let regex1 = /hello/gi;
let regex2 = /hello/gi;
let regex3 = regex1;

console.log("regex1 === regex2:", regex1 === regex2);
console.log("regex1 === regex3:", regex1 === regex3);

// Compare by properties
function regexEqual(r1, r2) {
    return r1.source === r2.source && r1.flags === r2.flags;
}

console.log("Content equal:", regexEqual(regex1, regex2));
console.log("regex1 source:", regex1.source);
console.log("regex2 source:", regex2.source);
console.log("regex1 flags:", regex1.flags);
console.log("regex2 flags:", regex2.flags);