How can I write a replace method for String in JavaScript?

Question

I heard, that string in JavaScript has immutability.

So, how can I write a method to replace some character in string?

What I want is:

String.prototype.replaceChar(char1, char2) {
 for (var i = 0; i < this.length; i++) {
 if (this[i] == char1) {
 this[i] = char2;
 }
 }
 return this;
}

Then, I can use it like this:

'abc'.replaceChar('a','b'); // bbc

I know it will not work, because the immutability of string.

But in native code, I can use the native replace method like this:

'abc'.replace(/a/g,'b');

I don't really know how to solve this problem.

• 001: replace returns a new string. It does not modify the original.
• Dwza: so you want to replace string/chars by reference ?

Answer 1

You can use the following approach:

String.prototype.replaceAll = function(search, replacement) {
 return this.replace(new RegExp(search, 'g'), replacement);
};

• Dekel: You don't even need a new variable, just use return this.replace(new RegExp(search, 'g'), replacement);
• Stephan Bijzitter: This is the same as 'abc'.replace(/a/g,'b');, except that it also invokes another function and creates a RegExp object.

Answer 2

You can use array, too:

String.prototype.replaceChar = function (char1, char2) {
newstr=[];
for (i = 0; i < this.length; i++) {
newstr.push(this[i]);
if (newstr[i] == char1) {
newstr[i] = char2
}
}
return newstr.join("");
}
console.log('abca'.replaceChar('a','G'));

Answer 3

If you want a solution without regex (as a way to learn), you can use the following:

String.prototype.replaceChar = function(char1, char2) {
 var s = this.toString();
 for (var i = 0; i < s.length; i++) {
 if (s[i] == char1) {
 s = s.slice(0, i) + char2 + s.slice(i+1);
 }
 }
 return s;
}
console.log('aaabaaa'.replaceChar('a', 'c'))

The idea is that you need this content of the string in a temp variable, then you need to go char-by-char, and if that char is the one you are looking for - you need to build your string again.