JavaScript RegExp ?! Quantifier

The RegExp ?!m Quantifier in JavaScript is used to find the match of any string which is not followed by a specific string m. 

Syntax: 

/?!m/ 

or

new RegExp("?!m")

Syntax with modifiers:

/\?!m/g 

or

new RegExp("?!m", "g")

Example 1: This example matches the words ‘Geeks’ not followed by 123 in the whole string. 

Javascript

function geek() {
    let str1 = "Geeks for 123 Geeks@";
    let regex4 = /Geeks(?!123)/g;
    let match4 = str1.match(regex4);

    console.log("Found " + match4.length
        + " matches: " + match4);
}
geek();

Output

Found 2 matches: Geeks,Geeks

Example 2: This example replaces the word ‘128’ with ‘#’. 

Javascript

function geek() {
    let str1 = "@128Geek128";
    let regex4 = new RegExp("128(?!ee)", "gi");
    let replace = "#";
    let match4 = str1.replace(regex4, replace);
    console.log(" New string: " + match4);
}
geek();

Output

 New string: @#Geek#

Supported Browsers: The browsers supported by RegExp ?! Quantifier are listed below:

• Google Chrome
• Apple Safari
• Mozilla Firefox
• Opera
• Internet Explorer

We have a complete list of Javascript RegExp expressions, to check those please go through this JavaScript RegExp Complete Reference article.

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.