code: function findIndex(arr, prop, value) {
    // use native findIndex if supported
    if (Array.prototype.findIndex) {
      return arr.findIndex(function (cur) {
        return cur[prop] === value;
      });
    }
  
    // use `find` + `indexOf` if `findIndex` isn't supported
    var match = find(arr, function (obj) {
      return obj[prop] === value;
    });
    return arr.indexOf(match);
  }
docs: Return the index of the matching object
  @method
  @memberof Popper.Utils
  @argument {Array} arr
  @argument prop
  @argument value
  @returns index or -1