How to replace a substring between two indices

Question

I want to replace text between two indices in Javascript, something like:

str = \"The Hello World Code!\";
str.replaceBetween(4,9,\"Hi\");
// outputs \"The          


        

Answer 1

A more robust version of VisioN's solution that detects out of range errors and throws meaningful and easy to debug RangeErrors. If you want, you can extend the String.prototype as well.

function replaceString(str, start, end, replace) {
  if (start < 0 || start > str.length) {
    throw new RangeError(`start index ${start} is out of the range 0~${str.length}`);
  }
  if (end > str.length || end < start) {
    throw new RangeError(`end index ${end} is out of the range ${start}~${str.length}`);
  }
  return str.substring(0, start) + replace + str.substring(end);
}

// replace in the middle of the string, replacement string can be any length
console.log(replaceString("abcdef", 2, 4, "hhhh")); // output: "abhhhhef"

// insert in the front of the string, start and end index equal to 0
console.log(replaceString("abcdef", 0, 0, "hhhh")); // output: "hhhhabcdef"

// append at the end of the string, start and end index equal to the length of the string
console.log(replaceString("abcdef", 6, 6, "hhhh")); // output: "abcdefhhhh"

// error 1: start index is greater than end index
// console.log(replaceString("abcdef", 4, 2, "hhhh")); // output: RangeError: end index 2 is out of the range 4~6

// error 2: start/end index is less than 0
// console.log(replaceString("abcdef", -2, 2, "hhhh")); // output: RangeError: start index -2 is out of the range 0~6

// error 3: start/end index is greater than length of the string
// console.log(replaceString("abcdef", 3, 20, "hhhh")); // output: RangeError: end index 20 is out of the range 3~6