awesome-string/src/manipulate/insert.js

The ultimate JavaScript string library

import coerceToNumber from 'helper/number/coerce_to_number';
import coerceToString from 'helper/string/coerce_to_string';

/**
 * Inserts into `subject` a string `toInsert` at specified `position`.
 *
 * @function insert
 * @static
 * @since 1.0.0
 * @memberOf Manipulate
 * @param {string} [subject=''] The string where to insert.
 * @param {string} [toInsert=''] The string to be inserted.
 * @param {number} [position=0] The position to insert.
 * @return {string} Returns the string after insertion.
 * @example
 * as.insert('ct', 'a', 1);
 * // => 'cat'
 *
 * as.insert('sunny', ' day', 5);
 * // => 'sunny day'
 */
export default function insert(subject, toInsert, position) {
  const subjectString = coerceToString(subject);
  const toInsertString = coerceToString(toInsert);
  const positionNumber = coerceToNumber(position);
  if (positionNumber < 0 || positionNumber > subjectString.length || toInsertString === '') {
    return subjectString;
  }
  return subjectString.slice(0, positionNumber) + toInsertString + subjectString.slice(positionNumber);
}