gistfile1.m

- (BOOL)webView:(UIWebView *)webView
        shouldStartLoadWithRequest:(NSURLRequest *)request
        navigationType:(UIWebViewNavigationType)navigationType {
    NSURL * url = [request URL];
    if ([[url scheme] isEqualToString:@"crab"]) {
        // 在这里做js调native的事情
        // ....
        // 做完之后用如下方法调回js
        [webView stringByEvaluatingJavaScriptFromString:@"window.command"];
        return NO;
    }
    return YES;
}