iOS call java script function

[knut]

HI All.
Can someone show me how call js function from objective c code ?
I try to use stringByEvaluatingJavaScriptFromString but in my js function I use timer so based on documentation i found that i only can use js call which is limited 10 second and I am in confused how call js function with timer?

JavaScript execution time is limited to 10 seconds for each top-level entry point. If your script executes for more than 10 seconds, Safari stops executing the script. This is likely to occur at a random place in your code, so unintended consequences may result. This limit is imposed because JavaScript execution may cause the main thread to block, so when scripts are running, the user is not able to interact with the webpage.