CODEWITHSUNDEEP
javascriptnode.jsregexstring
karlosuccess
karlosuccess

Reputation: 885

How to replace all occurrences of a string except the first one in JavaScript?

I have this string:

hello world hello world hello world hello

and I need to get the following:

hello world hello hello hello

If I use:

str = str.replace('world', '');

it only removes the first occurrence of world in the above string.

How can I replace all the occurrences of it except the first one?

Upvotes: 15

Views: 7602

Answers (6)

bobble bubble
bobble bubble

Reputation: 18490

Without additional function or lookarounds it can be done by using a variation of The Trick.

let str = 'hello world hello world hello world hello';

str = str.replace(/^(.*?world)|world/g, '$1');
console.log(str);

See this regex101 demo

The part from ^ start until the first occurance of world (lazy .*? between) gets captured by group one | OR any remaining worlds are normally matched. In this case the "trick" is to capture what is needed on the left side of the alternation | but match what is not needed on the right.

Replacement is $1 and contains the substing until the first world if the left side succeeded. Else if the right side matched, the first group would be empty - hence world gets removed.

Since nowadays lookbehind is available in JS regex, another idea is to replace (world)(?<=\1.+) with empty. It checks if the capture occurs before in the string and is not necessarily more efficient.

Upvotes: 1

Kristianmitk
Kristianmitk

Reputation: 4778

You can pass a function to String#replace, where you can specify to omit replacing the first occurrence. Also make your first parameter of replace a regex to match all occurrences.

Demo

let str = 'hello world hello world hello world hello',
    i = 0;
    
str = str.replace(/world/g, m  => !i++ ? m : '');
console.log(str);

Note

You could avoid using the global counter variable i by using a IIFE:

let str = 'hello world hello world hello world hello';

str = str.replace(/world/g, (i => m => !i++ ? m : '')(0));
console.log(str);

Upvotes: 20

Marcos Casagrande
Marcos Casagrande

Reputation: 40404

To provide an alternative to @Kristianmitk excellent answer, we can use a positive lookbehind, which is supported in Node.Js & Chrome >= 62

const string = 'hello world hello world hello world hello';

console.log(
  string.replace(/(?<=world[\s\S]+)world/g, '')
);
// or
console.log(
  string.replace(/(?<=(world)[\s\S]+)\1/g, '')
);

Using Symbol.replace well-known symbol.

The Symbol.replace well-known symbol specifies the method that replaces matched substrings of a string. This function is called by the String.prototype.replace() method.

const string = 'hello world hello world hello world hello';

class ReplaceButFirst {
     constructor(word, replace = '') {
         this.count = 0;
         this.replace = replace;
         this.pattern = new RegExp(word, 'g');
     }
     
     [Symbol.replace](str) {
          return str.replace(this.pattern, m => !this.count++ ? m : this.replace);
     }
}

console.log(
  string.replace(new ReplaceButFirst('world'))
);

Upvotes: 3

Zohaib Ijaz
Zohaib Ijaz

Reputation: 22885

In my solution, I am replacing first occurrence with a current timestamp, then replacing all occurrences and then finally replacing timestamp with world

You can also use str.split('world') and then join

var str = 'hello world hello world hello world hello';
var strs = str.split('world');
str = strs[0] + 'world' + strs.slice(1).join('');
console.log(str);


var str = 'hello world hello world hello world hello';

const d = Date.now()
str = str.replace('world', d).replace(/world/gi, '').replace(d, 'world');

console.log(str);

Upvotes: 1

Rama Adaikkalam
Rama Adaikkalam

Reputation: 733

var str = 'hello world hello world hello world hello'; 

var count = 0;
var result = str.replace(/world/gi, function (x) {
  if(count == 0) {
      count++;
      return x;
    } else {
      return '';	
    }
});

console.log(result);

Upvotes: 1

dave
dave

Reputation: 64657

I would do it like this:

  1. Get the substring up until and including the first occurrence.
  2. Append to that the substring after the first occurrence, with all other occurrences removed:

    function replaceExceptFirst(str, search) {
         let index = str.indexOf(search);
         return str.substring(0, index + search.length) + 
             str.substring(index + search.length).replace(/world/g, '')
    }
    
    console.log(replaceExceptFirst('hello world hello world world hello', 'world'))

Upvotes: 0

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