How to concatenate regex literals in JavaScript ?

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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 = " zambiatek |"
        + " A computer science portal for zambiatek"; 
  
    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: zambiatek | A computer science portal for zambiatekis 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 = /zambiatek/g; 
    var regex2 = / for zambiatek/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:

/zambiatek for zambiatek/gy

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