iOS Use UIWebView to execute JavaScript string using Math.pow

Question

I want to evaluate a string which is written in JavaScipt in iOS and learned I can to that by using: [self.webView stringByEvaluatingJavaScriptFromString:formula]

The code I'm using is:

NSString *formula = @"( 1.5 * Math.pow(2, 3) ) / 12"; formula = [NSString stringWithFormat:@"eval('%@')", formula]; NSInteger value = [[self.webView stringByEvaluatingJavaScriptFromString:formula] integerValue];

The problem is the Math.pow function. If I dont use it , I get a real value form the webView. If I have Math.pow in the string, I just get empty string back. Can anyone help me how to change the code so I can use strings which contains Math.pow?

did you try to wrap that into javascript method and execute f.e [[self.webView stringByEvaluatingJavaScriptFromString:@"javascript:myMethod();"] in your js method execute needed calculations and print output number — Injectios
– Injectios, Commented May 30, 2014 at 7:39
why do you need that -> you can execute such calculations natively — Injectios
– Injectios, Commented May 30, 2014 at 7:47

sergio · Accepted Answer · 2014-05-30 07:59:26Z

1

The problem is here:

NSInteger value = [[self.webView stringByEvaluatingJavaScriptFromString:formula] integerValue];

where you are converting your result in a integer value. So, it gets rounded off.

Correct would be:

float value = [[self.webView stringByEvaluatingJavaScriptFromString:formula] floatValue];

notice both the value type and the use of floatValue for the conversion from string.

BTW, you do not need the eval, strictly.

edited May 30, 2014 at 7:59

answered May 30, 2014 at 7:51

sergio

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2 Comments

Jonas Over a year ago

This has no effect on the JS result which is an empty string @"".

sergio Over a year ago

In my case it is working, I tested it before posting. If I use 24 instead of 12, I get 0.5

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