findIndex alternative for IE?

Question

I have this code for navigation scroll to section .

var lastId;
    var topMenu = $(".community-nav");   
    var topMenuHeight = topMenu.outerHeight() - 19; 
    if(window.matchMedia("(max-width: 768px)").matches){
        var logoHeight = $(".community-logo").outerHeight();
        var topMenuHeight =  topMenu.outerHeight() - logoHeight;
    };
    menuItems = topMenu.find('.community-links li > div'),
    scrollItems = $('.nav-section')


      menuItems.click(function(e){
        var href = $(this).attr("data-target");
        var currentItem = $(this);
        var sectionClass = $("#community-intranav");
        scrollPartialMenuItem(currentItem, sectionClass);    
        var offsetTop = href === "#" ? 0 : $(href).offset().top-topMenuHeight + 20;
         if(window.matchMedia("(max-width: 768px)").matches){


          };
        $('html, body').stop().animate({ 
            scrollTop: offsetTop
        }, 850);
        e.preventDefault();
      });

      function getCurrentSection(scrollPosition) {
        return scrollItems.toArray().findIndex(function(item) {
          return item.offsetTop < scrollPosition && item.offsetTop+item.clientHeight > scrollPosition;
        });
      }

    // Bind to scroll
    $(window).on("load scroll",function(e){    
        var scrollPosition = $(this).scrollTop()+topMenuHeight;
        var currentSection = getCurrentSection(scrollPosition) ;
        var id = currentSection > -1 ? scrollItems[currentSection].id : "";

        if (id && lastId !== id) {
        lastId = id;
        menuItems.removeClass("active");
        menuItems.filter("[data-target='#"+id+"']").addClass('active');
        }                   
     });

In the above code,the findIndex method is supported in IE.I want an alternative for the same so that I can rewrite my function getCurrentSection using something other than the findIndex method.Please help.

Answer 1

You can use a polly fill to add the missing features such as this.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findIndex#Polyfill

add this to your code

// https://tc39.github.io/ecma262/#sec-array.prototype.findindex
if (!Array.prototype.findIndex) {
  Object.defineProperty(Array.prototype, 'findIndex', {
    value: function(predicate) {
     // 1. Let O be ? ToObject(this value).
      if (this == null) {
        throw new TypeError('"this" is null or not defined');
      }

      var o = Object(this);

      // 2. Let len be ? ToLength(? Get(O, "length")).
      var len = o.length >>> 0;

      // 3. If IsCallable(predicate) is false, throw a TypeError exception.
      if (typeof predicate !== 'function') {
        throw new TypeError('predicate must be a function');
      }

      // 4. If thisArg was supplied, let T be thisArg; else let T be undefined.
      var thisArg = arguments[1];

      // 5. Let k be 0.
      var k = 0;

      // 6. Repeat, while k < len
      while (k < len) {
        // a. Let Pk be ! ToString(k).
        // b. Let kValue be ? Get(O, Pk).
        // c. Let testResult be ToBoolean(? Call(predicate, T, « kValue, k, O »)).
        // d. If testResult is true, return k.
        var kValue = o[k];
        if (predicate.call(thisArg, kValue, k, o)) {
          return k;
        }
        // e. Increase k by 1.
        k++;
      }

      // 7. Return -1.
      return -1;
    },
    configurable: true,
    writable: true
  });
}

Or you can make use of a pollyfill service cdn like pollyfill.io

 <script src='https://cdn.polyfill.io/v2/polyfill.js?features?feature=Array.prototype.findIndex'>
    </script>