In this post, you'll learn how to replace all string occurrences in JavaScript by splitting and joining a string, string.replace() combined with a global regular expression, and string.replaceAll().
Table of Contents
1. Splitting and joining an array
If you google how to "replace all string occurrences in JavaScript", the first approach you are likely to find is to use an intermediate array.
Here's how it works:
- Split the
stringintopiecesby thesearchstring:
const pieces = string.split(search);
- Then join the pieces putting the
replacestring in between:
const resultingString = pieces.join(replace);
For example, let's replace all spaces ' ' with hyphens '-' in 'duck duck go' string:
const search = ' ';const replaceWith = '-';const result = 'duck duck go'.split(search).join(replaceWith);console.log(result); // => 'duck-duck-go'
'duck duck go'.split(' ') splits the string into pieces: ['duck', 'duck', 'go'].
Then the pieces ['duck', 'duck', 'go'].join('-') are joined by inserting '-' in between them, which results in the string 'duck-duck-go'.
Here's a generalized helper function that uses splitting and joining approach:
function replaceAll(string, search, replace) { return string.split(search).join(replace);}console.log(replaceAll('abba', 'a', 'i')); // => 'ibbi'console.log(replaceAll('go go go!', 'go', 'move')); // => 'move move move!'console.log(replaceAll('oops', 'z', 'y')); // => 'oops'
This approach requires transforming the string into an array, and then back into a string. Let's continue looking for better alternatives.
2. replace() with a global regular expression
The string method string.replace(regExpSearch, replaceWith) searches and replaces the occurrences of the regular expression regExpSearch with replaceWith string.
To make the method replace() replace all occurrences of the pattern - you have to enable the global flag on the regular expression:
- Append
gto the end of regular expression literal:/search/g - Or when using a regular expression constructor, add
'g'to the second argument:new RegExp('search', 'g')
Let's replace all occurrences of ' ' with '-':
const searchRegExp = /\s/g;const replaceWith = '-';const result = 'duck duck go'.replace(searchRegExp, replaceWith);console.log(result); // => 'duck-duck-go'
The regular expression literal /\s/g (note the g global flag) matches the space ' '.
'duck duck go'.replace(/\s/g, '-') replaces all matches of /\s/g with '-', which results in 'duck-duck-go'.
You can easily make case insensitive replaces by adding i flag to the regular expression:
const searchRegExp = /duck/gi;const replaceWith = 'goose';const result = 'DUCK Duck go'.replace(searchRegExp, replaceWith);result; // => 'goose goose go'
The regular expression /duck/gi performs a global case-insensitive search (note i and g flags). /duck/gi matches 'DUCK', as well as 'Duck'.
Invoking 'DUCK Duck go'.replace(/duck/gi, 'goose') replaces all matches of /duck/gi substrings with 'goose'.
2.1 Regular expression from a string
When the regular expression is created from a string, you have to escape the characters - [ ] / { } ( ) * + ? . \ ^ $ | because they have special meaning within the regular expression.
Because of that, the special characters are a problem when you'd like to make replace all operation. Here's an example:
const search = '+';const searchRegExp = new RegExp(search, 'g'); // Throws SyntaxErrorconst replaceWith = '-';const result = '5+2+1'.replace(searchRegExp, replaceWith);
The above snippet tries to transform the search string '+' into a regular expression. But '+' is an invalid regular expression, thus SyntaxError: Invalid regular expression: /+/ is thrown.
Escaping the character '\\+' solves the problem. Try the fixed demo.
2.2 replace() with a string
If the first argument search of string.replace(search, replaceWith) is a string, then the method replaces only the first occurrence of search:
const search = ' ';const replace = '-';const result = 'duck duck go'.replace(search, replace);console.log(result); // => 'duck-duck go'
'duck duck go'.replace(' ', '-') replaces only the first appearance of a space.
3. replaceAll() method
Finally, the method string.replaceAll(search, replaceWith) replaces all appearances of search string with replaceWith.
Let's replace all occurrences of ' ' with '-':
const search = ' ';const replaceWith = '-';const result = 'duck duck go'.replaceAll(search, replaceWith);console.log(result); // => 'duck-duck-go'
'duck duck go'.replaceAll(' ', '-') replaces all occurrences of ' ' string with '-'.
string.replaceAll(search, replaceWith) is the best way to replace all string occurrences in a string
Note that browser support for this method is currently limited, and you might require a polyfill.
3.1 The difference between replaceAll() and replace()
The string methods replaceAll(search, replaceWith) and replace(search, replaceWith) work the same way, except 2 things:
- If
searchargument is a string,replaceAll()replaces all occurrences ofsearchwithreplaceWith, whilereplace()replaces only the first occurence - If
searchargument is a non-global regular expression, thenreplaceAll()throws aTypeErrorexception.
4. Key takeaway
The first approach to replacing all occurrences is to split the string into chunks by the search string and then join back the string, placing the replace string between the chunks: string.split(search).join(replaceWith). This approach works, but it's hacky.
Another approach is to use string.replace(/SEARCH/g, replaceWith) with a regular expression having the global flag enabled.
Unfortunately, you cannot easily generate regular expressions from a string at runtime, because the special characters of regular expressions have to be escaped.
Finally, the string method string.replaceAll(search, replaceWith) replaces all string occurrences.
I recommend using string.replaceAll() to replace strings.
What other ways to replace all string occurrences do you know? Please share in a comment below!
