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How to perform Multiline matching with JavaScript RegExp?
To perform multiline matching in JavaScript, use the m flag with regular expressions. This flag makes ^ and $ anchors match the beginning and end of each line, not just the entire string.
Syntax
/pattern/m
new RegExp("pattern", "m")
How the m Flag Works
Without the m flag, ^ matches only the start of the string and $ matches only the end. With the m flag, they match line boundaries created by
Example: Basic Multiline Matching
<html>
<head>
<title>JavaScript Regular Expression</title>
</head>
<body>
<script>
var myStr = "Welcome\ning!";
var reg = /^ing/m;
var match = myStr.match(reg);
document.write("Match found: " + match);
</script>
</body>
</html>
Match found: ing
Comparison: With and Without m Flag
let text = "First line\nSecond line\nThird line";
// Without m flag - only matches start/end of entire string
let withoutM = text.match(/^Second/);
console.log("Without m flag:", withoutM);
// With m flag - matches start/end of each line
let withM = text.match(/^Second/m);
console.log("With m flag:", withM);
Without m flag: null With m flag: Second
Finding All Line Beginnings
let multilineText = "apple\nbanana\ncherry";
// Find all words at line beginnings
let matches = multilineText.match(/^\w+/gm);
console.log("All line beginnings:", matches);
All line beginnings: ["apple", "banana", "cherry"]
Comparison Table
| Flag | ^ Matches | $ Matches | Use Case |
|---|---|---|---|
| No flag | Start of string only | End of string only | Single-line text |
m |
Start of each line | End of each line | Multiline text |
Conclusion
The m flag enables line-by-line pattern matching in multiline strings. Use it when you need to match patterns at the beginning or end of individual lines rather than the entire string.
Updated on: 2026-03-15T23:18:59+05:30
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