How to concatenate regex literals in JavaScript ?
Regex is a sequence of pattern that is used for matching with a pattern. While searching for data in a text, the search pattern is described for what we are searching for. It can be a single character or a more complex pattern. It can be used to perform all types of text searches. Regex has its own static and instance properties.
Syntax:
/pattern/modifiers
Example: A regular expression.
/gfg/g
Where,
- gfg is a pattern (to be used in a search).
- g is a modifier (modifies the search to be case-insensitive).
The concatenation of Regex in the programming world can be understood as combining text patterns
to obtain a new text pattern, such as “Hello” + “World” is /HelloWorld/. Whenever RegExp() is called, it creates a new RegExp object.
Example 1: This example creating an expression without actually using the Regex literal syntax. This allows you to make arbitrary string manipulation before it becomes a Regex object.
<!DOCTYPE html> <html> <head> <meta name="viewport" content= "width=device-width,initial-scale=1.0" /> <title> Concatenation of Regex </title> </head> <body> <h3>The concatenation of Regex </h3> <hr> <script> function gfg() { var segment_part = " GeeksforGeeks |" + " A computer science portal for geeks"; var pattern = new RegExp("GFG:" + /*comment here */ segment_part + /* that was defined just now */ "is a computer science portal"); document.write(pattern); } gfg(); </script> </body> </html> |
Output:
Example 2: If you have two Regex literals, you can concatenate them using a technique where it removes duplicates, but keep the unique values in order, joining both the regex literals.
Example: /hello/y + / world/g would be /hello world/gy
<!DOCTYPE html> <html> <head> <meta name="viewport" content= "width=device-width, initial-scale=1.0"/> <title> Concatenation of Regex </title> </head> <body> <h3>Concatenation of Regex </h3> <hr> <script> function gfg() { var regex1 = /geeks/g; var regex2 = / for geeks/y; var flags = (regex1.flags + regex2.flags).split("") .sort().join("") .replace(/(.)(?=.*\1)/g, ""); var regex3 = new RegExp(regex1.source + regex2.source, flags); document.write(regex3); } gfg(); </script> </body> </html> |
Output:
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