Get a javascript variable's value in iOS app

Question

I need to access a javascript variable which is declared inside a try block in the script

var ErrorResponse = "";

in my iOS app. I don't have much idea about javascript thats why I am unable to find out the way to do it. I am using this:

NSString *jsString = @"var temp = ErrorResponse; return temp";
NSString *myFieldValue1 = [self.viewYTParser stringByEvaluatingJavaScriptFromString:jsString];

to retrieve the value but it returns an empty string.

var ErrorResopnse = ""; is empty. Set a value to it like: var ErrorResopnse = "Foo"; — Midhun MP
– Midhun MP, Commented Dec 26, 2013 at 7:54
it is empty when it is initialized. It gets set with a value later in the code — brainforked
– brainforked, Commented Dec 26, 2013 at 7:55

Michael Kessler · Accepted Answer · 2013-12-26 08:30:27Z

3

Here is the code that should do the magic:

NSString *errorResponse = [self.viewYTParser stringByEvaluatingJavaScriptFromString:@"ErrorResponse"];

Just execute this line each time you need to retrieve the up-to-date value of ErrorResponse.

You shouldn't use the return keyword.
If you want your JS to return any value from stringByEvaluatingJavaScriptFromString then it should be something that you would regularly write after the return keyword in regular JS function - without the return word itself.

edited Dec 26, 2013 at 8:30

answered Dec 26, 2013 at 8:24

Michael Kessler

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7 Comments

Michael Kessler Over a year ago

Are you sure that this variable has value at the moment you execute this line?

brainforked Over a year ago

Yes. And just for checking I also initialized it var ErrorResopnse = "something"; but still didn't get anything

brainforked Over a year ago

I figured out what the problem was. It was not accessible because it was declared locally. I declared it as a global variable and it worked. But now the trouble is that I am not supposed to make changes in the script and I will have to access the local variable. How can I do this?

san Over a year ago

Create a global variable and keep the local variable as it is. Assign value of local variable to global variable and then use stringByEvaluatingJavaScriptFromString

brainforked Over a year ago

@san Hi, I could have done it but as I said in comment above that I am not supposed to change the script.

|

Retro · Accepted Answer · 2013-12-26 07:55:03Z

0

// simplified expression, no function needed
NSString *expr = @"document.getElementById('myDiv').offsetHeight / document.getElementById('myDiv').style.lineHeight";
// now pass it to the web view and parse the result
int lines = [[self.webView stringByEvaluatingJavaScriptFromString:expr] intValue];

answered Dec 26, 2013 at 7:55

Retro

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