Fastest method to replace all instances of a character in a string

javascript

regex

string-manipulation

javascript-features

byNikita Barsukov·Feb 7, 2025

The quickest way to replace every instance of a character in a string? Call on String.prototype.replace backed by a global regex (/g). Its efficiency and simplicity just can't be beat.

let str = "example-string";
// Prepare for 'y' invasion as all 'x'; result: "eyample-string"
let newStr = str.replace(/x/g, 'y');

Substitute x with your target and y with the desired replacement for an instant full-string resolution.

Deep-dive explanation

Robust pattern matching with regex

Need a solution for more complex character replacements? Break out JavaScript's RegExp object. Crafted to work hand-in-glove with replace methods, it enables you to create intricate patterns matching strings and sub-strings ripe for replacement.

let story = "The quick brown fox jumps over the lazy dog";
// All vowels are now undercover as '*'; result: "Th* q**ck br*wn f*x j*mps *v*r th* l*zy d*g"
let newStory = story.replace(/[aeiou]/g, '*');

Balancing performance

While .replace() with the global flag /g is generally the fastest kid on the block, .replaceAll() is worth considering if you're working with strict string replacements that throw up a 'No Entry' sign to regex patterns.

Case-insensitive and multiple-character substitutions

If case-insensitivity is your jam, or you're dealing with multi-character targets, bring the /i flag and broader regex patterns into the mix. For multi-characters, [ ] defines a character set-out for replacement in a single command.

let greeting = "Hello, World!";
// 'o' is offended and runs away, '0' takes its place; result: "Hell0, W0rld!"
let newGreeting = greeting.replace(/o/gi, '0');

Practical tips and edge handling

Replacing special characters and spaces

Special characters such as ., ?, * must be escaped with a backslash (\) in your regex, and \s is the ticket for dealing with spaces.

let specialStr = "End. Stop? Pause...";
// Periode gets a loud voice, '..' becomes '!!'; result: "End! Stop? Pause!!!"
let newSpecialStr = specialStr.replace(/\./g, '!');

Tackling empty strings and null values

Empty strings or null values in your strings can cause havoc. Avoid undefined pain by checking your string's existence before making a move.

function safeReplace(originalStr, searchValue, newValue) {
  // Don't mess with me, null and undefined!
  if (!originalStr) return originalStr; 
  return originalStr.replace(new RegExp(searchValue, 'g'), newValue);
}

Conquering complex pattern matching

Dealing with tricky patterns or circumstances? Expand your regex arsenal with lookaheads and capture groups for replacements based on conditions and context within your string.

Solid reliability

Remember, regex-based methods are like a good dog. They've been tested and trusted across different browsers and platforms. Go ahead, use them. They won't bite.

Best practices with a pinch of sugar

Escapade from regex characters

Creating regex patterns on the fly often involves escaping special regex characters to dodge burning bridges.

function escapeRegExp(string) {
  //I solemnly swear that I am up to no good.
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

Replacements with function callbacks

Yes, .replace() can handle a function as its second argument and, boy, it's a welcome callback when runtime string manipulation is on the menu.

let info = "Image: img-01.png";
// Img-01.png has gained a level!; result: "Image: img-02.png"
let newInfo = info.replace(/-(\d+)/g, (match, num) => `-${String(Number(num) + 1).padStart(2, '0')}`);