UICWebView(OC)とJS(JavaScript)は相互作用します.

  
JSContext* context = [webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"];
   context       webview context       ，  context       js    。

      Apple   Api  JSContext ，       JSContext       。    ，        API          。

/**
    private api                 jscontext    ；     web     script，                

 @param unused class  WebView
 @param ctx   UIWebView   JSContext  
 @param frame  WebFrameLoadDelegate   WebKit WebFrame
 */
- (void) webView: (id) unused didCreateJavaScriptContext: (JSContext*) ctx forFrame: (id) frame
{
    
    NSString *frameMehtod = [NSString stringWithUTF8String:webFrameBase64Str];
    NSData *frameData = [[NSData alloc]initWithBase64EncodedString:frameMehtod options:NSDataBase64DecodingIgnoreUnknownCharacters];
    NSString *frameStr = [[NSString alloc]initWithData:frameData encoding:NSUTF8StringEncoding];
    SEL frameSelector = NSSelectorFromString(frameStr);
    //     only interested in root-level frames
    if ([frame respondsToSelector:frameSelector] && [frame parentFrame] != nil ) {
        return;
    }
    
    void (^didCreateJavaScriptContext)() = ^{
        
        for (UIWebView *webv in webviews) {
            
            NSString *webIdentifier =  [NSString stringWithFormat:@"rain_jsWebView_%lud",(NSUInteger)webv.hash];
            
            NSString *jsAddVariable = [NSString stringWithFormat:@"var %@ = '%@'",webIdentifier,webIdentifier];
            
            [webv stringByEvaluatingJavaScriptFromString:jsAddVariable];// webView          
            
            JSValue *identifierJSValue = ctx[webIdentifier];//              [ctx objectForKeyedSubscript:webIdentifier];
            
            if ([identifierJSValue.toString isEqualToString:webIdentifier]) {
                [webv rainDidCreateJavaScriptContext:ctx];
                return ;
            }
            
        }
        
    };
    
    if ([NSThread isMainThread]) {
        didCreateJavaScriptContext();
    }else {
        dispatch_async(dispatch_get_main_queue(), didCreateJavaScriptContext);
        
    }
    
}

/*     ，      JSContext  webview      ，        */

- (void)webViewDidFinishLoad:(UIWebView *)webView {
   
 [self.webView.context evaluateScript:@"jsFunction('native   js   ')"];
 
}


/*     ，  jscontext jsvalue   */
- (void)webViewDidFinishLoad:(UIWebView *)webView {
    
  JSValue *jsFunctionValue = self.webView.context[@"jsFunction"];
   [jsFunctionValue callWithArguments:@[@"native   js   "]];

}
/*     ：  webview  */
- (void)webViewDidFinishLoad:(UIWebView *)webView {
    
     [self.webView stringByEvaluatingJavaScriptFromString:@"jsFunction('native   js   ')"];

}

a、  block  
self.webview.context[@"jsCallNative"] = ^(NSString *message){
  NSLog(message);
}
 h5     jsCallNative('    Native   ')   

b、  JSExport    
       JSExport  ，          JS   ，    JS                  


    JSExport   
@protocol RainJSExportProtocol

/**
 js          ，  native    

 @param log js          
 @param void js     native    
 @return void
 */
JSExportAs(log, - (void)debugLog:(NSString *)message);

/**
 js            

 @param callNative js       
 @param void js callNative         
 @return void
 */
JSExportAs(callNative, - (void)callInterface:(NSString *)interface parameters:(NSString *)jsonStr);


//          ，  js         ：         ；
//   -(void)myName:(NSString *)name age:(NSString *)myage height:(NSString *)myheight; js  native         native.myNameAgeHeight('name','15','172')

@end

      RainJSExportProtocol    

#pragma mark-- RainJSExportProtocol

- (void)debugLog:(NSString *)message {
    
#ifdef DEBUG
    
    NSLog(@"%@",message);
    
#endif
    
}

- (void)callInterface:(NSString *)interface parameters:(NSString *)jsonStr {
    
    NSLog(@"interface %@  jsonStr %@",interface,jsonStr);
    
}

     JS     native  ：context[@"native"] = self;// self   jscontext       

 js       

native.log('    ');
native. callNative('     ','     ');