“SyntaxError: Unexpected EOF” when evaluating JavaScript in iOS UIWebView

Question

I keep getting this error in JavaScript when trying to pass some JSON to a UIWebView:

SyntaxError: Unexpected EOF

There is no line number or filename available in window.onerror but I've already checked all referenced files, and they are fine.

I'm using MonoTouch EvaluateJavaScript method which is equivalent to ObjC stringByEvaluatingJavaScriptFromString::

webView.EvaluateJavascript(
    "Viewer.init($('#page'), " + json.ToString() + ");"
);

It works just fine on “simple” JSON input but breaks at larger objects.
What could go wrong?

Answer 1

Before passing an NSString to a UIWebView, be sure to escape newlines as well as single/double quotes:

NSString *html = @"<div id='my-div'>Hello there</div>";

html = [html stringByReplacingOccurrencesOfString:@"\'" withString:@"\\\'"];
html = [html stringByReplacingOccurrencesOfString:@"\"" withString:@"\\\""];
html = [html stringByReplacingOccurrencesOfString:@"\n" withString:@"\\n"];
html = [html stringByReplacingOccurrencesOfString:@"\r" withString:@""];

NSString *javaScript = [NSString stringWithFormat:@"injectSomeHtml('%@');", html];
[_webView stringByEvaluatingJavaScriptFromString:javaScript];

Answer 2

Apparently, I forgot to escape newlines in JSON, and thus created an “unexpected EOF” for UIWebView.