appear-polyfill/lib/index.js

[](https://www.npmjs.com/package/rax-appear)

"use strict";

exports.__esModule = true;
exports.setupAppear = setupAppear;
exports.setupPreAppear = setupPreAppear;
var _intersectionObserverManager = require("./intersectionObserverManager");
/**
 * Simulate appear & disappear events.
 */

// hijack Node.prototype.addEventListener
var injectEventListenerHook = function (events, Node, observerElement) {
  if (events === void 0) {
    events = [];
  }
  var nativeAddEventListener = Node.prototype.addEventListener;
  Node.prototype.addEventListener = function (eventName, eventHandler, useCapture) {
    var lowerCaseEventName = eventName && String(eventName).toLowerCase();
    var isAppearEvent = events.some(function (item) {
      return item === lowerCaseEventName;
    });
    if (isAppearEvent) observerElement(this);
    nativeAddEventListener.call(this, eventName, eventHandler, useCapture);
  };
  return function () {
    Node.prototype.addEventListener = nativeAddEventListener;
    (0, _intersectionObserverManager.destroyAllIntersectionObserver)();
  };
};
function setupPreAppear(win, options) {
  var observerElement = (0, _intersectionObserverManager.createIntersectionObserver)(_intersectionObserverManager.IntersectionObserverMode.PRE_APPEAR, options);
  injectEventListenerHook(['preappear'], win.Node, observerElement);
}
function setupAppear(win, options) {
  if (!win) {
    if (typeof window !== 'undefined') {
      win = window;
    } else {
      return;
    }
  }
  if (options != null && options.preAppear) {
    setupPreAppear(win, options);
  }
  var observerElement = (0, _intersectionObserverManager.createIntersectionObserver)(_intersectionObserverManager.IntersectionObserverMode.DEFAULT, options);
  return injectEventListenerHook(['appear', 'disappear'], win.Node, observerElement);
}