iOS js调webview的alert 为什么弹出来点击不了

NSString* methodNameStr=[NSString
stringWithFormat:@"device_callback(%d,\"%@\")",[@"6001"
isEqualToString:@"6001"]?-1:-2,[@"6001"
isEqualToString:@"6001"]?@"支付取消":@"支付失败"];

如果在通知方法里直接调用

 [weakSelf.webView
stringByEvaluatingJavaScriptFromString:methodNameStr];
会弹出alert  但是点击不了  

所以不能这样写 

 NSString *jsMyAlert =[NSString
stringWithFormat:@"setTimeout(function(){%@;},1)",methodNameStr];
 [weakSelf.webView stringByEvaluatingJavaScriptFromString:jsMyAlert];