line-splitter.js

/**
 * Function that separates a string value to line by symbols length;
 *
 * @param {String} string - input string
 * @param {Number} lineLength - symbols length per line
 * @param {Boolean} useSpaces - Take into account the gaps or not
 * @returns {Array.<String>}
 */
const lineSplitter = (string, lineLength, useSpaces = true) => {
  let result = [];
  let frmString = string;
  let lastSpaceRgx = /\s(?!.*\s)/;

  while(frmString.length > 0) {
    let line = frmString.substring(0, lineLength);
    let nextIdx = lineLength;
    
    if (useSpaces) {
      // if space mod on, find the last space index and set as end index of substring
      let idx = line.search(lastSpaceRgx);
      
      if (idx > 0) {
        line = line.substring(0, idx);
        nextIdx = idx;
      }
    }

    frmString = frmString.substring(nextIdx);
    result.push(line);
  }

  return result;
};

// Example
const loremTest = "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy";
const result = lineSplitter(loremTest, 20);
console.log(result);  // result ["Lorem Ipsum is", " simply dummy text", " of the printing", " and typesetting", " industry. Lorem", " Ipsum has been the", " industry's", " standard", " dummy"]