Javascript using .replace() at a specific index of the search

user_10533464 0
Viewed 1321

Is there a function that can replace a string within a string once at a specific index of the string? Example:

var string1="my text is my text and my big text";
var string2="my";
string1.replaceAt(string2,"your",2);

and the resultant output would be "my text is my text and your big text"

javascript
5 Answers

You can do this with a little bit of manipulation, not requiring any regex.

I used this function to fetch the position (index) of another string within a string.

From there, it's as simple as returning a substring from the beginning to the found index, injecting your replacement, and then returning the rest of the string.

function replaceAt(s, subString, replacement, index) {
  const p = s.split(subString, index+1).join(subString);
  return p.length < s.length ? p + replacement + s.slice(p.length + subString.length) : s;
}

console.log(replaceAt("my text is my text and my big text", "my", "your", 2))
console.log(replaceAt("my text is my text and that's all", "my", "your", 2))
console.log(replaceAt("my text is my my my my text", "my", "your", 2))

user_48756310

There's not a built-in way to do that, but you can exploit the fact that .replace() can be passed a function:

let count = 0;
console.log("my text is my text and my big text".replace(/my/g, function() {
  if (count++ === 2) return "your";
  return "my";
}));
The function is passed the matched string and any groups as arguments, but in this case that's not really necessary.

user_1826680

Here is a prototype version

String.prototype.replaceAt = function(str1,str2,pos) {
  let count = 0;
  let re = new RegExp(str1,"g");
  return this.replace(re, function() {
    return (count++ === pos) ? str2 : str1;
  });
}
console.log("my text is my text and my big text".replaceAt("my","your",2))

user_2957830

Beside the use of a function for replacement, you could use the given variable for the position directly for decrementing and take this value as check for replacement or not.

const replace = (string, s, r, p) => string.replace(new RegExp(s, 'g'), m => p-- ? m : r);
var string = 'my text is my text and my big text';

console.log(replace(string, 'my', 'your', 2));

user_14476750

As we need to look for index where we need to replace our word and for other words we don't need any change so used "map". Converted string to array by split and using map returned each element as it is and just replaced word when reached to specific index (by logic of index-- == 0). Finally joined back array to string.

    function replace(text, strFrom, strTo, index) {
     return text.split(' ')
                   .map(d => d == strFrom && index-- == 0
                                 ? strTo 
                                 : d)
                   .join(' ')
    }
    
    var string = 'my text is my text and my big text';
    
    string = replace(string, 'my', 'your', 2)
    
    console.log(string)

user_30484290
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