phpjs/functions/strings/substr_replace.js

php.js offers community built php functions in javascript

function substr_replace(str, replace, start, length) {
  // From: http://phpjs.org/functions
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: substr_replace('ABCDEFGH:/MNRPQR/', 'bob', 0);
  // *     returns 1: 'bob'
  // *     example 2: $var = 'ABCDEFGH:/MNRPQR/';
  // *     example 2: substr_replace($var, 'bob', 0, $var.length);
  // *     returns 2: 'bob'
  // *     example 3: substr_replace('ABCDEFGH:/MNRPQR/', 'bob', 0, 0);
  // *     returns 3: 'bobABCDEFGH:/MNRPQR/'
  // *     example 4: substr_replace('ABCDEFGH:/MNRPQR/', 'bob', 10, -1);
  // *     returns 4: 'ABCDEFGH:/bob/'
  // *     example 5: substr_replace('ABCDEFGH:/MNRPQR/', 'bob', -7, -1);
  // *     returns 5: 'ABCDEFGH:/bob/'
  // *     example 6: substr_replace('ABCDEFGH:/MNRPQR/', '', 10, -1)
  // *     returns 6: 'ABCDEFGH://'

  if (start < 0) { // start position in str
    start = start + str.length;
  }
  length = length !== undefined ? length : str.length;
  if (length < 0) {
    length = length + str.length - start;
  }

  return str.slice(0, start) + replace.substr(0, length) + replace.slice(length) + str.slice(start + length);
}