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.
Javascript
function gfg() { var segment_part = " neveropen |" + " A computer science portal for neveropen"; var pattern = new RegExp("GFG:" + /*comment here */ segment_part + /* that was defined just now */ "is a computer science portal"); console.log(pattern); } gfg(); |
Output:
/GFG: neveropen | A computer science portal for neveropenis a computer science portal/
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
Javascript
function gfg() { var regex1 = /neveropen/g; var regex2 = / for neveropen/y; var flags = (regex1.flags + regex2.flags).split("") .sort().join("") .replace(/(.)(?=.*\1)/g, ""); var regex3 = new RegExp(regex1.source + regex2.source, flags); console.log(regex3); } gfg(); |
Output:
/neveropen for neveropen/gy
