index.js

(function(root) {
  var isOn = false;
  var scrollbarSize;
  var scrollTop;

  function getScrollbarSize() {
    if (typeof scrollbarSize !== 'undefined') return scrollbarSize;

    var doc = document.documentElement;
    var dummyScroller = document.createElement('div');
    dummyScroller.setAttribute('style', 'width:99px;height:99px;' + 'position:absolute;top:-9999px;overflow:scroll;');
    doc.appendChild(dummyScroller);
    scrollbarSize = dummyScroller.offsetWidth - dummyScroller.clientWidth;
    doc.removeChild(dummyScroller);
    return scrollbarSize;
  }

  function hasScrollbar() {
    return document.documentElement.scrollHeight > window.innerHeight;
  }

  function on(options) {
    if (typeof document === 'undefined' || isOn) return;
    var doc = document.documentElement;
    scrollTop = window.pageYOffset;
    if (hasScrollbar()) {
      doc.style.width = 'calc(100% - '+ getScrollbarSize() +'px)';
    } else {
      doc.style.width = '100%';
    }
    doc.style.position = 'fixed';
    doc.style.top = -scrollTop + 'px';
    doc.style.overflow = 'hidden';
    isOn = true;
  }

  function off() {
    if (typeof document === 'undefined' || !isOn) return;
    var doc = document.documentElement;
    doc.style.width = '';
    doc.style.position = '';
    doc.style.top = '';
    doc.style.overflow = '';
    window.scroll(0, scrollTop);
    isOn = false;
  }

  function toggle() {
    if (isOn) {
      off();
      return;
    }
    on();
  }

  var noScroll = {
    on: on,
    off: off,
    toggle: toggle,
  };

  if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
    module.exports = noScroll;
  } else {
    root.noScroll = noScroll;
  }
})(this);