背景

来自我司业务方要求，需开发一款APP。但由于时间限制，只能采取套壳app方式，即原生app内嵌webview展示前端页面。本文主要记述JavaScript与原生app间通信，以及内嵌webview开发时，前端方面可能踩的一些坑。

技术架构

前端：vue+vuex+vue-router+webpack全家桶开发
后端：Node(express框架)简单转发接口至java-真后端接口。

js与原生通信

采用jsBridge技术和原生APP通信
android 传送门和ios 传送门，因为两个平台初始化方式不同，因此在开发过程中，需针对每个平台做对应操作。具体做法

按照库要求，声明好初始化函数

//android
function connectWebViewJavascriptBridge{
    if (window.WebViewJavascriptBridge) {
            //do your work here
        } else {
            document.addEventListener(
                'WebViewJavascriptBridgeReady'
                , function() {
                    //do your work here
                },
                false
            );
        }
}
//ios
setupWebViewJavascriptBridge(function(bridge) {
	
	/* Initialize your app here */

	bridge.registerHandler('JS Echo', function(data, responseCallback) {
		console.log("JS Echo called with:", data)
		responseCallback(data)
	})
	bridge.callHandler('ObjC Echo', {'key':'value'}, function responseCallback(responseData) {
		console.log("JS received response:", responseData)
	})
})

初始化，得到bride对象。则可调用原生app已定义方法或注册js方法供原生调用

setupWebViewJavascriptBridge(function(bridge) {
	
	/* Initialize your app here */

	bridge.registerHandler('JS Echo', function(data, responseCallback) {
		console.log("JS Echo called with:", data)
		responseCallback(data) // 
	})
	bridge.callHandler('ObjC Echo', {'key':'value'}, function responseCallback(responseData) {
		console.log("JS received response:", responseData)
	})
})

Tips:

Android 与 IOS初化方式不同，需要判断平台后再进行调用。另外Android初始化时，需额外引入一些方法。
调用Android定义方法时，返回值只能为字符串。而IOS可为JSON对象。需要在callHandler时，对返回值进行封装处理或统一规定好数据格式。
完整业务代码文末给出

踩坑

调用bridge属性方法registerHandler,callHandler，在回调函数内处理页面逻辑时，最好避免使用this
vue组件下，在registerHandler，callHandler回调函数内使用vue实例时,无法获取实例对象。正确做法是在回调函数内调用window对象下方法，再通过该方法去使用vue实例对象。

//vue 组件
mounted(){
    window['handleServicePushMessage'] = (res) => {
    	vm.handleServicePushMessage(res)
    };
    bridge.registerHandler("servicePushMessage", function (data, responseCallback) {
        handleServicePushMessage(data)
        responseCallback(data) //可传值到App
    })
}

桌面推送消息点击跳转至App内详情情况下，js注册方法供调用时，可能会引起重复调用的问题。故在方法内需做好重复调用判断
IOS-12.0版本下，在有输入框的页面，输入时软键盘会顶起webview，当失去焦点时，webview不会自动回弹。需调用APP做处理拉回界面。

//解决ios 12版本 ui不自动回拉问题
document.addEventListener('focusout', function (event) {
	let curTarget = event.target || event.srcElement;
	let isInput= ['input', 'textarea'];
	//处理页面连续点击都为输入框的情况
	let curTargetTagName= curTarget.tagName.toLowerCase();
	    if (isInput.includes(curTargetTagName)) {
    	    //事件处理
    	    //延迟获取activeElement再进行判断
        	setTimeout(function () {
        	    let activeEle = document.activeElement;
        	    let activeEleTagName= activeEle.tagName.toLowerCase();
        	    if (!isInput.includes(activeEleTagName)) {
        	        // console.log(document.activeElement.tagName);
        	        //调用app桥拉回webview
        	        performMethod('scrollTotop', null);
                    }
        	}, 200);
        }
}, true);

5.当js调用app不存在的桥时，无法捕获异常，页面不会报错
6.导航栏显示问题，由于项目时间紧迫，并且app开发人员不承载太多开发任务，所以路由控制放在前端处理。此时就有导航栏电池时间栏的适配问题。本项目采用顶部下调20PX处理，电池时间栏字体颜色的控制也是通过桥调用来设置；另外iPhone X适配另外处理。
7.当app加载完网页时，js立即调用原生方法桥时，可能出现原生方法桥未注册完情况。故特殊情况需延迟调用桥操作。

完整代码

/*判断平台*/
function (window) {
	window.device = {};
	var ua = navigator.userAgent;
	var android = ua.match(/(Android);?[\s\/]+([\d.]+)?/);
	var ipad = ua.match(/(iPad).*OS\s([\d_]+)/);
	var ipod = ua.match(/(iPod)(.*OS\s([\d_]+))?/);
	var iphone = !ipad && ua.match(/(iPhone\sOS)\s([\d_]+)/);
	device.ios = device.android = device.iphone = device.ipad = device.androidChrome = false;
	if (android) {
		device.os = 'android';
		device.osVersion = android[2];
		device.android = true;
		device.androidChrome = ua.toLowerCase().indexOf('chrome') >= 0
	}
	if (ipad || iphone || ipod) {
		device.os = 'ios';
		device.ios = true
	}
}(window)
/*引入Android需要的初始化，IOS不执行，如执行IOS端桥调用会受影响*/
(function () {
	if (window.WebViewJavascriptBridge || device.ios) {
		return false;
	}
	var messagingIframe;
	var sendMessageQueue = [];
	var receiveMessageQueue = [];
	var messageHandlers = {};
	var CUSTOM_PROTOCOL_SCHEME = 'yy';
	var QUEUE_HAS_MESSAGE = '__QUEUE_MESSAGE__/';
	var responseCallbacks = {};
	var uniqueId = 1;

	function _createQueueReadyIframe(doc) {
		messagingIframe = doc.createElement('iframe');
		messagingIframe.style.display = 'none';
		doc.documentElement.appendChild(messagingIframe);
	}

	/*set default messageHandler*/
	function init(messageHandler) {
		if (WebViewJavascriptBridge._messageHandler) {
			throw new Error('WebViewJavascriptBridge.init called twice');
		}
		WebViewJavascriptBridge._messageHandler = messageHandler;
		var receivedMessages = receiveMessageQueue;
		receiveMessageQueue = null;
		for (var i = 0; i < receivedMessages.length; i++) {
			_dispatchMessageFromNative(receivedMessages[i]);
		}
	}

	function send(data, responseCallback) {
		_doSend({data: data}, responseCallback);
	}

	function registerHandler(handlerName, handler) {
		messageHandlers[handlerName] = handler;
	}

	function callHandler(handlerName, data, responseCallback) {
		_doSend({handlerName: handlerName, data: data}, responseCallback);
	}

	/*sendMessage add message, 触发native处理 sendMessage*/
	function _doSend(message, responseCallback) {
		if (responseCallback) {
			var callbackId = 'cb_' + (uniqueId++) + '_' + new Date().getTime();
			responseCallbacks[callbackId] = responseCallback;
			message.callbackId = callbackId;
		}
		sendMessageQueue.push(message);
		messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + '://' + QUEUE_HAS_MESSAGE;
	}

	/* 提供给native调用,该函数作用:获取sendMessageQueue返回给native,由于android不能直接获取返回的内容,所以使用url shouldOverrideUrlLoading 的方式返回内容*/
	function _fetchQueue() {
		var messageQueueString = JSON.stringify(sendMessageQueue);
		sendMessageQueue = [];
		/*android can't read directly the return data, so we can reload iframe src to communicate with java*/
		messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + '://return/_fetchQueue/' + encodeURIComponent(messageQueueString);
	}

	/*提供给native使用,*/
	function _dispatchMessageFromNative(messageJSON) {
		setTimeout(function () {
			var message = JSON.parse(messageJSON);
			var responseCallback;
			/*java call finished, now need to call js callback function*/
			if (message.responseId) {
				responseCallback = responseCallbacks[message.responseId];
				if (!responseCallback) {
					return;
				}
				responseCallback(message.responseData);
				delete responseCallbacks[message.responseId];
			} else {/*直接发送*/
				if (message.callbackId) {
					var callbackResponseId = message.callbackId;
					responseCallback = function (responseData) {
						_doSend({responseId: callbackResponseId, responseData: responseData});
					};
				}
				var handler = WebViewJavascriptBridge._messageHandler;
				if (message.handlerName) {
					handler = messageHandlers[message.handlerName];
				}
				/*查找指定handler*/
				try {
					handler(message.data, responseCallback);
				} catch (exception) {
					if (typeof console != 'undefined') {
						console.log("WebViewJavascriptBridge: WARNING: javascript handler threw.", message, exception);
					}
				}
			}
		});
	}

	/*提供给native调用,receiveMessageQueue 在会在页面加载完后赋值为null,所以*/
	function _handleMessageFromNative(messageJSON) {
		if (receiveMessageQueue && receiveMessageQueue.length > 0) {
			receiveMessageQueue.push(messageJSON);
		} else {
			_dispatchMessageFromNative(messageJSON);
		}
	}

	var WebViewJavascriptBridge = window.WebViewJavascriptBridge = {
		init: init,
		send: send,
		registerHandler: registerHandler,
		callHandler: callHandler,
		_fetchQueue: _fetchQueue,
		_handleMessageFromNative: _handleMessageFromNative
	};
	var doc = document;
	_createQueueReadyIframe(doc);
	var readyEvent = doc.createEvent('Events');
	readyEvent.initEvent('WebViewJavascriptBridgeReady');
	readyEvent.bridge = WebViewJavascriptBridge;
	doc.dispatchEvent(readyEvent);
})();
/*Android端初始化函数*/
function connectWebViewJavascriptBridge(callback) {
	if (window.WebViewJavascriptBridge) {
		callback(WebViewJavascriptBridge)
	} else {
		document.addEventListener('WebViewJavascriptBridgeReady', function () {
			callback(WebViewJavascriptBridge)
		}, false);
	}
}
/*IOS端初始化函数*/
function setupWebViewJavascriptBridge(callback) {
	if (window.WebViewJavascriptBridge) {
		return callback(WebViewJavascriptBridge)
	} else {
	}
	if (window.WVJBCallbacks) {
		return window.WVJBCallbacks.push(callback)
	}
	window.WVJBCallbacks = [callback];
	var WVJBIframe = document.createElement('iframe');
	WVJBIframe.style.display = 'none';
	WVJBIframe.src = 'wvjbscheme://__BRIDGE_LOADED__';
	document.documentElement.appendChild(WVJBIframe);
	setTimeout(function () {
		document.documentElement.removeChild(WVJBIframe)
	}, 0)
}
if(device.ios){
    setupWebViewJavascriptBridge(function(bridge){
        /*挂载上全局对象*/
        window.BRIDGE= brige;
    })
}
if(device.android){
    connectWebViewJavascriptBridge(function(bridge){
        /*挂载上全局对象*/
        window.BRIDGE= brige;
    })
}