CODEWITHSUNDEEP
javascriptregexreplace
Mystical
Mystical

Reputation: 2783

JavaScript regex replace all parts of a string except parts that contain a specific string

Let's say I had the following string Hello World and I wanted to replace every part of it that does not contain an o or a space with an x. Using regex, I could simply do the following:

var myStr = "Hello World";
console.log(myStr.replace(/[^o ]/g, "x"));

Now, what if I wanted to replace all parts of a string that does not contain the string ll or a space for example, with an x? I tried this but with no luck:

// intended result: xxllx xxxxx
var myStr = "Hello World";
console.log(myStr.replace(/[^ll ]/g, "x"));

It seems to be interpreting the ll as separate characters and not a character sequence. How would I go about solving this with regex and using the replace method?

Upvotes: 1

Views: 83

Answers (2)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626689

Match and capture what you want to keep, match everything else to replace:

var myStr = "Hello World";
console.log(myStr.replace(/(ll| )|[\s\S]/g, (x,y) => y || "x"));

Before ES6+:

var myStr = "Hello World";
    console.log(myStr.replace(/(ll| )|[\s\S]/g, function (x,y) {
        return y || "x";
    })
);

So, (ll| )|[\s\S] matches and captures into Group 1 ll or a space, or just matches any char with [\s\S] (you may use [^] (in any JS environment) or a . with /s modifier (in ECMAScript2018+ compatible environments)) and if Group 1 matches (y in the above code), it is returned back. Else, replace with x.

Upvotes: 1

anubhava
anubhava

Reputation: 784948

You may use this pure regex solution using look-arounds:

var str = 'Hello World';

var re = /(?<!l)l(?!l)|[^l ]/g;

var repl = str.replace(re, 'x');

console.log(repl);
//=> xxllx xxxxx

RegEx Details:

  • (?<!l)l(?!l): Match l if it is not followed and preceded by another l
  • |; OR
  • [^l ]: Match any character that is not l and not a space

Online RegEx Demo

Upvotes: 2

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