Develop Reference

Add a java program to run within the Android Studio app

I am just a side programmer, working on little tiny projects for some extra coin. Nothing to big.
But I got this code with an if and else if statement that I am trying to run on the GUI on Android Studio, I want the code to display within the actual android app. I don't know where to put the code in or how to call it in the .java file, so that it can run in the android app on the Studio program. I was hoping maybe someone with more experience with Android Studio can help me figure out what my next steps are. I do apologize if I am vague with my problem, I am not quite great at explaining the issue.
public class Main {
public static void main(String[] args) {
String lit;
Scanner scan = new Scanner(System.in);
System.out.println("Set the thermostat to call for heating, does the pilot stay lit? y/n");
lit = scan.nextLine();
if (lit.equals("y")) {
System.out.println("Great. So it works.");
} else if (lit.equals("n")) {
System.out.println("Check the thermocouple.");
}
}
}

Android apps work in a different way to 'normal' java programs, the concept of System.in doesn't really exist. The main function isn't something that you call manually. User input comes from having widgets on the screen like an EditText to read the data.
I'd start here to get a grasp on a basic app and then you should be able to see how you could modify your sample above to an app.

I see you need to make an actual GUI app with this.
I would suggest you to see some tutorials on android studio first.
To build this app, first put in 2 Textview, and 2 buttons in the activity_main.
In the properties panel on the left, change the text of these objects so that your question is in one textView, the other is blank and the buttons are labelled Yes or No (or y and n, your choice).
Change the id of the 2 buttons so that one's id is yes and the other's is no. Set the id of the blank textView as result.
Now, in the main activity, put this in BEFORE #Override:
Button yes = (Button) findViewById(R.id.yes);
Button no = (Button) findViewById(R.id.no);
TextView result = (TextView) findViewById(R.id.result);
And put this AFTER setContentView (on the next line):
yes.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
result.setText("Whatever your message is for yes");
}
no.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
result.setText("Whatever your message is for no");
}
I hope this is what you wanted. Once again, I would advise you to watch some tutorials.

Android Apps have no CUI console.
You must implement those outputs through Android's GUI APIs, for example, TextView, Toast or etc.

Selenium-Java-geckodriver : Test Execution halts with JavaScript error as "document.getElementById(...) is null"

I had been encountering this issue for a while now. Browsed through a lot of threads on SO & other forums but still clueless.
While automating a simple flow on a Web Application with Selenium 3.4.0, geckodriver v0.16.1 & Mozilla Firefox 53.0 within Eclipse Neon v2 IDE, I am facing an error intermittently on the console as:
JavaScript error: https://www.url.com/my, line 1715: TypeError: document.getElementById(...) is null
Though using chromedriver v2.29/Google Chrome 58.0 or using Python I don't face any such issue.
Once this error appears, the Test Execution halts and finally shows TimeoutException as follows:
Exception in thread "main" org.openqa.selenium.TimeoutException: Timeout loading page after 300000ms
URL of the website is: https://www.shareinvestor.com/my
The HTML DOM is:
<div id="sic_sitemap">
<div id="sic_container">
<div id="sic_header">
<h1 id="sic_siteTitle">
<div id="sic_headerMembershipLink">
<a id="sic_mobileEdition" href="/mobile">
<div id="sic_loginContainer" class="sic_logIn" style="">
<div class="sic_login-wrap">
<div class="sic_logIn-subscribe">
<div class="sic_logIn-bg">
<a href="/user/login.html">
</div>
</div>
</div>
</div>
<div id="sic_subHeader">
<div id="sic_mainNav" class="sic_withRightCorner">
<div id="sic_sideBar" class="sic_expanded { selected_market_suffix: 'MY'}">
<div class="sic_superBanner sic_superBannerTop">
<div id="sic_content" class="sic_collapsed">
<div id="sic_footer" class="si_fixed">
</div>
As of now, I have tried out the following options but of no avail:
Java Click
JavascriptExecutor Click
Actions Click
Here is my code:
import org.openqa.selenium.By;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.interactions.Actions;
import org.openqa.selenium.remote.DesiredCapabilities;
public class 78644072022 {
public static void main(String[] args) {
System.setProperty("webdriver.gecko.driver", "C:\\Utility\\BrowserDrivers\\geckodriver.exe");
DesiredCapabilities dc = DesiredCapabilities.firefox();
dc.setCapability("marionette", true);
WebDriver driver = new FirefoxDriver(dc);
driver.manage().window().maximize();
driver.get("https://www.shareinvestor.com/my");
WebElement login_button = driver.findElement(By.xpath("//div[#id='sic_loginContainer']/div/div[#class='sic_logIn-bg']/a"));
//Java Click
login_button.click();
//JavascriptExecutor Click
/*JavascriptExecutor jse = (JavascriptExecutor)driver;
jse.executeScript("arguments[0].click();", login_button);*/
//Actions Click
/*Actions act = new Actions(driver);
act.moveToElement(login_button).click().build().perform();*/
driver.findElement(By.xpath("//input[#id='sic_login_header_username']")).sendKeys("debanjan");
driver.findElement(By.xpath("//input[#id='sic_login_header_password']")).sendKeys("5786");
driver.findElement(By.xpath("//input[#id='sic_login_submit']")).click();
}
}
I am looking for a Java Solution with geckodriver to overcome the error JavaScript error:TypeError: document.getElementById(...) is null
In one of the SO threads I saw a solution like:
You need to do a null check in updateHTML like this:
function updateHTML(elmId, value) {
var elem = document.getElementById(elmId);
if(typeof elem !== 'undefined' && elem !== null) {
document.getElementById(elmId).innerHTML = value;
}
}
Can we implement this?
Any suggestions & pointers will be helpful.

I am looking for a Java Solution with geckodriver to overcome the error JavaScript error:TypeError: document.getElementById(...) is null
To answer your question, I don't believe there's anything you can do to "fix" this via Java/Selenium. This is a JavaScript error, which originates from the website that you are trying to access. You might want to consider contacting their support team, maybe one of their developers can look at this issue.
Instead of clicking on the login button, maybe consider navigating directly to the login page?
driver.get("https://www.shareinvestor.com/user/login.html");

Firstly, Those javascript errors are not triggered due to any of the selenium code. Ofcourse, the timeout has been triggered by the selenium(will discuss on this on a later point).
You will get that javascript error irrespective of any kind of browser you launch the URL with. But in case of the gecko, you are notified in the eclipse console with but not in case of Chrome. If you need to see the java script error in chrome, just launch the url in chrome and go to devtools/console(F12). You can also see the same in firefox console too.
Chrome Img:
Secondly, We are getting timeout exception because the site is really taking too much time to load. I have been waited for 7 minutes and the page is still loading even now. Selenium won't executes its script unless the page has been completely launched. As a result we are getting timeout exception(not sure about the default page launch time permitted). I thought of bypassing directly to the login page ("https://www.shareinvestor.com/user/login.html") and that's also not taking any finite time to load completely.
Intepolation: Those java script errors are not an issue for automation But those page loads are really. This site doesn't seems like a good candidate for automation with this issue.
Update1: otherwise we can also stop the page loading via another thread like sending "esc" key sequence using Action class.
Update2: I tried the same code today and it works fine. Below is the code snippet that i have tried(There is no change at all)
public static void main(String[] args) throws InterruptedException
{
System.setProperty("webdriver.gecko.driver", "F:\\Softwares\\Selenium\\Webdriver\\geckodriver.exe");
WebDriver driver = new FirefoxDriver();
driver.manage().window().maximize();
driver.manage().timeouts().implicitlyWait(5, TimeUnit.SECONDS);
driver.get("https://www.shareinvestor.com/my");
WebElement login_button = driver.findElement(By.xpath("//div[#id='sic_loginContainer']/div/div[#class='sic_logIn-bg']/a"));
//Java Click
login_button.click();
System.out.println("In Login PAge");
driver.findElement(By.xpath("//input[#id='sic_login_header_username']")).sendKeys("debanjan");
driver.findElement(By.xpath("//input[#id='sic_login_header_password']")).sendKeys("5786");
System.out.println("Entered password");
driver.findElement(By.xpath("//input[#id='sic_login_submit']")).click();
}
Selenium version - 3.4.0
Gecko driver - v0.16.1(mine is 32 bit)
Mozilla - 51.0.1 (Update=>It's working on 53.02 also)
Hope this helps you. Thanks.

I think I've managed to find what is causing this uproar in your script.
I inspected your HTML and it seems javascript method function showRemaining() is causing this problem; because showRemaining() contains this statement
document.getElementById('countdown').innerHTML = '';
where it tries to set innerHTML attribute for element having id as countdown to ''.
But countdown doesn't exist anywhere on your web page hence the error.
TypeError: document.getElementById(...) is null
and somehow selenium isn't able to look past this error. So I think getting it fixed from developers should help you.
UPDATE :
Basically you need to wait all elements to load using implicit wait, once all elements are loaded, then your Javascript error gets resolved and ultimately interaction with the webpage is not hindered by that javascript error:
driver.get("https://www.shareinvestor.com/my");
driver.manage().timeouts().implicitlyWait(20, TimeUnit.SECONDS);
driver.manage().window().maximize();
/*String script = "function updateHTML(countdown, value) {" +
"var elem = document.getElementById('countdown');"+
"if(typeof elem !== 'undefined' && elem !== null) {"+
" document.getElementById('countdown').innerHTML = value;"+
"}"+
"}";
((JavascriptExecutor) driver).executeScript(script);*/
WebElement login_button = driver.findElement(By.xpath("//div[#id='sic_loginContainer']/div/div[#class='sic_logIn-bg']/a"));
login_button.click();
driver.findElement(By.xpath("//input[#id='sic_login_header_username']")).sendKeys("debanjan");
driver.findElement(By.xpath("//input[#id='sic_login_header_password']")).sendKeys("5786");
driver.findElement(By.xpath("//input[#id='sic_login_submit']")).click();

It looks like the XPath for the login_button is incorrect:
By.xpath("//div[#id='sic_loginContainer']/div/div[#class='sic_logIn-bg']/a");
Should be:
By.xpath("//div[#id='sic_loginContainer']/div/div/div[#class='sic_logIn-bg']/a");
This may explain the TimeoutException, since Selenium is unable to locate the non-existent element. EDIT: My mistake, you should see a NoSuchElementException if the element cannot be located.
As for the JavaScript error, unless you were trying to use Selenium to access the web element being manipulated by the JavaScript code (id='countdown' element), Selenium should just ignore the error. Otherwise, there's the potential for other Selenium errors, such as StaleElementReferenceException, but that does not seem to be the case.

This is due to your application HTML page using the async javascript and it uses some variable reference that is not available at the time of execution. we had same issue and asked developer to follow some best practices for javascript in the HTML like putting the script tag at end of the page. I have checked the HTML page source of the site and it contains many script tags in between the code. This will block the DOM rendering. Better, ask the developer to follow some best practices to include script tag in HTML. you refer the link Where should I put <script> tags in HTML markup? for the best practices.

Could someone once and for all please explain Cannot call determinedVisibility() - never saw a connection for the pid

I'm currently working on graphing data via d3 into a webview. Naturally, things are breaking as soon as I try to reload the graph and feed it new data. This lovely line keeps popping up: W/cr_BindingManager: Cannot call determinedVisibility() - never saw a connection for the pid.
I've scoured SO for an explanation, but there doesn't seem to be anything conclusive. People are just suggesting to turn on DOM storage in webview settings (which obviously doesn't fix the issue). I'm suspecting there is a race condition between reloading the graph and feeding it new data. I've overridden onPageFinished() in my WebViewClient to call the listener to load the data into the chart, thinking it would resolve the race condition, but to no avail.
Can someone please explain to me what W/cr_BindingManager: Cannot call determinedVisibility() - never saw a connection for the pid means? Am I off in my assessment? How can I debug it?
Any tips are appreciated.
EDIT: I've solved the original issue, but I would still love to learn what that line means. Bounty up.

Consecutive calls to loadUrl cause a race condition. The problem is that loadUrl("file://..") doesn't complete immediately, and so when you call loadUrl("javascript:..") it will sometimes execute before the page has loaded.
This is how I setup my webview:
wv = (CustomWebView) this.findViewById(R.id.webView1);
WebSettings wv_settings = wv.getSettings();
//this is where you fixed your code I guess
//And also by setting a WebClient to catch javascript's console messages :
wv.setWebChromeClient(new WebChromeClient() {
public boolean onConsoleMessage(ConsoleMessage cm) {
Log.d(TAG, cm.message() + " -- From line "
+ cm.lineNumber() + " of "
+ cm.sourceId() );
return true;
}
});
wv_settings.setDomStorageEnabled(true);
wv.setWebViewClient(new WebViewClient() {
#Override
public void onPageFinished(WebView view, String url) {
super.onPageFinished(view, url);
setTitle(view.getTitle());
//do your stuff ...
}
#Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if (url.startsWith("file"))
{
// Keep local assets in this WebView.
return false;
}
}
});
//wv.setWebViewClient(new HelpClient(this));//
wv.clearCache(true);
wv.clearHistory();
wv_settings.setJavaScriptEnabled(true);//XSS vulnerable
wv_settings.setJavaScriptCanOpenWindowsAutomatically(true);
wv.loadUrl("file:///android_asset/connect.php.html");
NOTE this line wv.setWebChromeClient(new WebChromeClient());
In API level 19 (Android 4.4 KitKat), the browser engine switched from Android webkit to chromium webkit, with almost all the original WebView API's wrapped to the counterparts of chromium webkit.
This is the method that gives the error (BindingManagerImpl.java), from Chromium source:
#Override
public void determinedVisibility(int pid) {
ManagedConnection managedConnection;
synchronized (mManagedConnections) {
managedConnection = mManagedConnections.get(pid);
}
if (managedConnection == null) {
Log.w(TAG, "Cannot call determinedVisibility() - never saw a connection for the pid: "
+ "%d", pid);
return;
}
It's a rendering warning from content.
You can dig around forever in that github source code, might be nice to see where the method determinedVisibility (in BindingManagerImpl.java) is called from...(suffix “Impl” for Implementation).
Hope this helps ;O)

This usually pops up when you are overriding the method shouldOverrideUrlLoading().
From my WebView usages on prior apps, this is due to what is being rendered on the WebView, what is being caught on the above method and in turn ignored.
I see this a lot when the websites that I load attempt to load scripts outside of the allowed domain.

Reloading and debugging JavaScript in TVOS simulator

I have started looking at tutorials for making TVML/TVJS based apps for the new Apple TV, and I have two problems that makes the development process very tedious and impractical.
First thing I am having trouble understanding is how I am supposed to debug code that happens on startup of the application. I have connected the Safari debugger, and I do manage to hit some breakpoints, but only for code that is triggered by some user input. On startup I am loading an xml document from a remote location, and I will use this to dynamically generate the tvml template, but I cannot get the debugger to stop anywhere in the code that is running before the template is done rendering.
The other anti-productive problem I have is that I cannot seem to reload the JavaScript files in any other way than completely shutting down the application in the simulator (double-click the home button, and swipe the app away). This also makes the debugger quit, so I have to restart that one as well. This surely cannot be the way you are supposed to do continuous development and testing?

You can make the debugger stop at the first line when you choose the Auto Pause and Auto Show options from the Safari menu "Develop/Simulator".
You are correct about the exit issue.
One thing you can also try is to run App.reload() from the Safari Debugger console.
This also restarts the app, maybe in the future they can make it work so the debugger will not be gone.
But at the moment this also does not solve the issue.

For manual debugger output (aka console.log()), you could redirect the logging to the Xcode debugger.
(somewhere on the web) I found a way to actually do that, in short it looks like...
AppDelegate.Swift
func appController(appController: TVApplicationController, evaluateAppJavaScriptInContext jsContext: JSContext) {
let jsInterface: cJsInterface = cJsInterface();
jsContext.setObject(jsInterface, forKeyedSubscript: "swiftInterface")
}
App.js
// re-route console.log() to XCode debug window
var console = {
log: function() {
var message = '';
for(var i = 0; i < arguments.length; i++) {
message += arguments[i] + ' '
};
swiftInterface.log(message)
}
};
JsInterface.Swift
#objc protocol jsInterfaceProtocol : JSExport {
func log(message: String) -> Void
}
...
class cJsInterface: NSObject, jsInterfaceProtocol {
func log(message: String) -> Void {
print("JS: \(message)")
}
}
Complete sources in github: https://github.com/iBaa/PlexConnectApp/tree/f512dfd9c1cb2fbfed2da43c4e3837435b0b22af
I don't have any solution for the dying debugger myself...

Detecting JavaScript errors in a UIWebView [duplicate]

I need to have my iPhone Objective-C code catch Javascript errors in a UIWebView. That includes uncaught exceptions, syntax errors when loading files, undefined variable references, etc.
This is for a development environment, so it doesn't need to be SDK-kosher. In fact, it only really needs to work on the simulator.
I've already found used some of the hidden WebKit tricks to e.g. expose Obj-C objects to JS and to intercept alert popups, but this one is still eluding me.
[NOTE: after posting this I did find one way using a debugging delegate. Is there a way with lower overhead, using the error console / web inspector?]

I have now found one way using the script debugger hooks in WebView (note, NOT UIWebView). I first had to subclass UIWebView and add a method like this:
- (void)webView:(id)webView windowScriptObjectAvailable:(id)newWindowScriptObject {
// save these goodies
windowScriptObject = newWindowScriptObject;
privateWebView = webView;
if (scriptDebuggingEnabled) {
[webView setScriptDebugDelegate:[[YourScriptDebugDelegate alloc] init]];
}
}
Next you should create a YourScriptDebugDelegate class that contains methods like these:
// in YourScriptDebugDelegate
- (void)webView:(WebView *)webView didParseSource:(NSString *)source
baseLineNumber:(unsigned)lineNumber
fromURL:(NSURL *)url
sourceId:(int)sid
forWebFrame:(WebFrame *)webFrame
{
NSLog(#"NSDD: called didParseSource: sid=%d, url=%#", sid, url);
}
// some source failed to parse
- (void)webView:(WebView *)webView failedToParseSource:(NSString *)source
baseLineNumber:(unsigned)lineNumber
fromURL:(NSURL *)url
withError:(NSError *)error
forWebFrame:(WebFrame *)webFrame
{
NSLog(#"NSDD: called failedToParseSource: url=%# line=%d error=%#\nsource=%#", url, lineNumber, error, source);
}
- (void)webView:(WebView *)webView exceptionWasRaised:(WebScriptCallFrame *)frame
sourceId:(int)sid
line:(int)lineno
forWebFrame:(WebFrame *)webFrame
{
NSLog(#"NSDD: exception: sid=%d line=%d function=%#, caller=%#, exception=%#",
sid, lineno, [frame functionName], [frame caller], [frame exception]);
}
There is probably a large runtime impact for this, as the debug delegate can also supply methods to be called for entering and exiting a stack frame, and for executing each line of code.
See http://www.koders.com/noncode/fid7DE7ECEB052C3531743728D41A233A951C79E0AE.aspx for the Objective-C++ definition of WebScriptDebugDelegate.
Those other methods:
// just entered a stack frame (i.e. called a function, or started global scope)
- (void)webView:(WebView *)webView didEnterCallFrame:(WebScriptCallFrame *)frame
sourceId:(int)sid
line:(int)lineno
forWebFrame:(WebFrame *)webFrame;
// about to execute some code
- (void)webView:(WebView *)webView willExecuteStatement:(WebScriptCallFrame *)frame
sourceId:(int)sid
line:(int)lineno
forWebFrame:(WebFrame *)webFrame;
// about to leave a stack frame (i.e. return from a function)
- (void)webView:(WebView *)webView willLeaveCallFrame:(WebScriptCallFrame *)frame
sourceId:(int)sid
line:(int)lineno
forWebFrame:(WebFrame *)webFrame;
Note that this is all hidden away in a private framework, so don't try to put this in code you submit to the App Store, and be prepared for some hackery to get it to work.

I created a nice little drop-in category that you can add to your project...
It is based on Robert Sanders solution. Kudos.
You can dowload it here:
UIWebView+Debug
This should make it a lot easier to debug you UIWebView :)

I used the great solution proposed from Robert Sanders: How can my iPhone Objective-C code get notified of Javascript errors in a UIWebView?
That hook for webkit works fine also on iPhone. Instead of standard UIWebView I allocated derived MyUIWebView. I needed also to define hidden classes inside MyWebScriptObjectDelegate.h:
#class WebView;
#class WebFrame;
#class WebScriptCallFrame;
Within the ios sdk 4.1 the function:
- (void)webView:(id)webView windowScriptObjectAvailable:(id)newWindowScriptObject
is deprecated and instead of it I used the function:
- (void)webView:(id)sender didClearWindowObject:(id)windowObject forFrame:(WebFrame*)frame
Also, I get some annoying warnings like "NSObject may not respond -windowScriptObject" because the class interface is hidden. I ignore them and it works nice.

One way that works during development if you have Safari v 6+ (I'm uncertain what iOS version you need) is to use the Safari development tools and hook into the UIWebView through it.
In Safari: Enable the Develop Menu (Preferences > Advanced > Show Develop menu in menu bar)
Plug your phone into the computer via the cable.
List item
Load up the app (either through xcode or just launch it) and go to the screen you want to debug.
Back in Safari, open the Develop menu, look for the name of your device in that menu (mine is called iPhone 5), should be right under User Agent.
Select it and you should see a drop down of the web views currently visible in your app.
If you have more than one webview on the screen you can try to tell them apart by rolling over the name of the app in the develop menu. The corresponding UIWebView will turn blue.
Select the name of the app, the develop window opens and you can inspect the console. You can even issue JS commands through it.

Straight Forward Way: Put this code on top of your controller/view that is using the UIWebView
#ifdef DEBUG
#interface DebugWebDelegate : NSObject
#end
#implementation DebugWebDelegate
#class WebView;
#class WebScriptCallFrame;
#class WebFrame;
- (void)webView:(WebView *)webView exceptionWasRaised:(WebScriptCallFrame *)frame
sourceId:(int)sid
line:(int)lineno
forWebFrame:(WebFrame *)webFrame
{
NSLog(#"NSDD: exception: sid=%d line=%d function=%#, caller=%#, exception=%#",
sid, lineno, [frame functionName], [frame caller], [frame exception]);
}
#end
#interface DebugWebView : UIWebView
id windowScriptObject;
id privateWebView;
#end
#implementation DebugWebView
- (void)webView:(id)sender didClearWindowObject:(id)windowObject forFrame:(WebFrame*)frame
{
[sender setScriptDebugDelegate:[[DebugWebDelegate alloc] init]];
}
#end
#endif
And then instantiate it like this:
#ifdef DEBUG
myWebview = [[DebugWebView alloc] initWithFrame:frame];
#else
myWebview = [[UIWebView alloc] initWithFrame:frame];
#endif
Using #ifdef DEBUG ensures that it doesn't go in the release build, but I would also recommend commenting it out when you're not using it since it has a performance impact. Credit goes to Robert Sanders and Prcela for the original code
Also if using ARC you may need to add "-fno-objc-arc" to prevent some build errors.

I have created an SDK kosher error reporter that includes:
The error message
The name of the file the error happens in
The line number the error happens on
The JavaScript callstack including parameters passed
It is part of the QuickConnectiPhone framework available from the sourceForge project
There is even an example application that shows how to send an error message to the Xcode terminal.
All you need to do is to surround your JavaScript code, including function definitions, etc. with try catch. It should look like this.
try{
//put your code here
}
catch(err){
logError(err);
}
It doesn't work really well with compilation errors but works with all others. Even anonymous functions.
The development blog is here
is here and includes links to the wiki, sourceForge, the google group, and twitter. Maybe this would help you out.

I have done this in firmware 1.x but not 2.x.
Here is the code I used in 1.x, it should at least help you on your way.
// Dismiss Javascript alerts and telephone confirms
/*- (void)alertSheet:(UIAlertSheet*)sheet buttonClicked:(int)button
{
if (button == 1)
{
[sheet setContext: nil];
}
[sheet dismiss];
}*/
// Javascript errors and logs
- (void) webView: (WebView*)webView addMessageToConsole: (NSDictionary*)dictionary
{
NSLog(#"Javascript log: %#", dictionary);
}
// Javascript alerts
- (void) webView: (WebView*)webView runJavaScriptAlertPanelWithMessage: (NSString*) message initiatedByFrame: (WebFrame*) frame
{
NSLog(#"Javascript Alert: %#", message);
UIAlertSheet *alertSheet = [[UIAlertSheet alloc] init];
[alertSheet setTitle: #"Javascript Alert"];
[alertSheet addButtonWithTitle: #"OK"];
[alertSheet setBodyText:message];
[alertSheet setDelegate: self];
[alertSheet setContext: self];
[alertSheet popupAlertAnimated:YES];
}

See exception handling in iOS7:
http://www.bignerdranch.com/blog/javascriptcore-example/
[context setExceptionHandler:^(JSContext *context, JSValue *value) {
NSLog(#"%#", value);
}];

First setup WebViewJavascriptBridge ,
then override console.error function.
In javascript
window.originConsoleError = console.error;
console.error = (msg) => {
window.originConsoleError(msg);
bridge.callHandler("sendConsoleLogToNative", {
action:action,
message:message
}, null)
};
In Objective-C
[self.bridge registerHandler:#"sendConsoleLogToNative" handler:^(id data, WVJBResponseCallback responseCallback) {
NSString *action = data[#"action"];
NSString *msg = data[#"message"];
if (isStringValid(action)){
if ([#"console.error" isEqualToString:action]){
NSLog(#"JS error :%#",msg);
}
}
}];

A simpler solution for some cases might be to just add Firebug Lite to the Web page.