JS Text Injecting Challenge.js

/* 

const originalText = 'Hello World';
const widgets = [
  {position: 2, text: '111'},
  {position: 4, text: '222'},
  {position: 6, text: '333'}
];

Given text and widgets, need to inject widget text in positions.

Result must be: He111ll222o 333World
*/



Object.assign(String.prototype, {
 injectWidgets(widgets) {
      const parts = [];
      const text = this.toString();

      let lastPosition = 0;
      widgets.forEach(widget => {
        parts.push(text.substr(lastPosition, widget.position - lastPosition));
        parts.push(widget.text);
        lastPosition = widget.position;
      });  
      parts.push(text.substr(lastPosition));

      return parts.join('');
  }
});

const injectedText = originalText.injectWidgets(widgets);

widgets.forEach(function (widget, index) {
    (index === widgets.length - 1) 
      ? newWord += originalText.substring(widget.position, originalText.length) 
      : newWord += originalText.substring(widgets[index - 1] 
          ? widgets[index - 1].position 
          : lastElem, widget.position) + widget.text;
});