How to extend a WebView with a Custom JSContext

WebViewWithCustomJsContext.mm

//how to extend a webview with custom Javascript functions
.....
#import <JavaScriptCore/JavaScriptCore.h>
#import <JavaScriptCore/JSBase.h>
.....
_webview.mainFrame.javaScriptContext[@"download"] = ^(NSString *url) {
    //do something
};


NSMutableArray *fileList = [[NSMutableArray alloc]init];
[fileList addObject:plugin.settings[@"video.mp4"]];

self.mainFrame.javaScriptContext[@"file"] = fileList;

//now you can access in javascript the file array
//or run the download function
.....