fix the iframe issue & clean up code style

autoHeightWebView/common.js

 export function getScript(props, getBaseScript, getIframeBaseScript) {
   const { hasIframe, files, customStyle, customScript, style } = getReloadRelatedData(props);
   const baseScript = getBaseScript(style);
-  let script = hasIframe ? getIframeBaseScript(style) : baseScript;
+  let script = hasIframe && getIframeBaseScript ? getIframeBaseScript(style) : baseScript;
   script = files ? appendFilesToHead(files, baseScript) : baseScript;
   script = appendStylesToHead(customStyle, script);
   customScript && (script = customScript + script);

autoHeightWebView/index.android.js

     };
     if (enableAnimation) {
       Object.assign(state, {
-        heightValue: new Animated.Value(initHeight + heightOffset),
+        heightValue: new Animated.Value(initHeight ? initHeight + heightOffset : 0),
         widthValue: new Animated.Value(initWidth)
       });
     }
       if (enableAnimation) {
         Animated.parallel([
           Animated.timing(heightValue, {
-            toValue: height + heightOffset,
+            toValue: height ? height + heightOffset : 0,
             easing: animationEasing,
             duration: animationDuration
           }),
     ${commonScript}
     var width = ${getWidth(style)};
     function updateSize() {
-      if(document.body.offsetHeight !== height || document.body.offsetWidth !== width) {
-        var size = getSize(document.body.firstChild); 
-        height = size.height;
-        width = size.width;
-        AutoHeightWebView.send(JSON.stringify({ width, height }));
-      }
+      var size = getSize(document.body.firstChild); 
+      height = size.height;
+      width = size.width;
+      AutoHeightWebView.send(JSON.stringify({ width, height }));
     }
     (function () {
       AutoHeightWebView.onMessage = updateSize;
     ${commonScript}
     var width = ${getWidth(style)};
     function updateSize() {
-      if(document.body.offsetHeight !== height || document.body.offsetWidth !== width) {
-        var size = getSize(document.body.firstChild); 
-        height = size.height;
-        width = size.width;
-        window.postMessage(JSON.stringify({ width, height }), '*');
-      }
+      var size = getSize(document.body.firstChild); 
+      height = size.height;
+      width = size.width;
+      window.postMessage(JSON.stringify({ width, height }), '*');
     }
     (function () {
       document.addEventListener("message", updateSize);

autoHeightWebView/index.ios.js

 
 import React, { PureComponent } from 'react';
 
-import { Animated, Easing, StyleSheet, ViewPropTypes, WebView } from 'react-native';
+import { Animated, StyleSheet, ViewPropTypes, WebView } from 'react-native';
 
 import PropTypes from 'prop-types';
 
   isSizeChanged,
   handleSizeUpdated,
   domMutationObserveScript,
-  getCurrentSize,
-  getRenderSize
+  getCurrentSize
 } from './common.js';
 
 import momoize from './momoize';