Methods of JavaScript injection using Objective-C

Question

I'm looking for different methods of injecting JavaScript into a WebView (in Cocoa).

I am trying to inject some javascript into the <head> tag of a HTML file that has been loaded into the WebView.

The following method doesn't work for me. It seems to only work with very simple JavaScript with no nested brackets (from what I have tested):

[webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"var script = document.createElement('script');"
                                                     "script.type = 'text/javascript';"
                                                     "script.text = \"some simple JavaScript"
                                                     "}\";"
                                                     "document.getElementsByTagName('head')[0].appendChild(script);"]];

Are there any other ways of doing this with more complicated JavaScript / jQuery functions?

The full code I am trying to inject is as follows:

function submitFormForTime(time){
    $(\".t_h\").each(function(i, obj) {
        if ($(this).text() != time) return;
        $(this).parent().find(\"form\").each(function(i, obj){
            obj.submit();
        });
    });
}

score 8 · Accepted Answer · edited May 23 '17 at 12:06

You can't use jQuery to add <script> tags. This has been asked many times. See:

You can do it with browser built-in functions, BUT:

Would it work to just assign your function to a variable on your page and then evaluate it? Something like:

-(void)webViewDidFinishLoad:(UIWebView *)webView
{
    // add function to page:
    NSString * js = @"myFunction = function(){ return \"success!\"; }" ;
    [ webView stringByEvaluatingJavaScriptFromString:js ] ;

    // execute newly added function:
    NSString * result = [ webView stringByEvaluatingJavaScriptFromString:@"myFunction();"] ;
    NSLog(@"result=\"%@\"", result) ;
}

update explicit examples:

You should use my above example as a template!

Anyway, there's 2 parts to the process... The Javascript part and the Objective-C part. At the Javascript level, you are doing this:

// assign a function to the variable "someFunction":
var someFunction = function(){...};

// call the function in the variable "someFunction":
someFunction();

You can also do it without assigning the function to a variable, for example, if you don't care about referring to the function in the future. Doing it without a variable and using an anonymous function looks like this:

( function(){...} )() ;

i.e. instead of doing var A = <the function>; A(); you are doing (<the function>)();

Finally, if your anonymous function takes arguments, like yours does, the pattern looks like this:

( function(var0, ..., varN){...} )(arg0, ..., argN);

Using that as a template for your code, your JS ends up like:

( function(time) {
    $(\".t_h\").each(function(i, obj) 
    {
        if ($(this).text() != time)  return;

        $(this).parent().find(\"form\").each(function(i, obj) {
            obj.submit();
        });
    });
})( 123.456 );

So, that's what you want the web view to execute... That's the code we pass to the webview. But you have to build that string in your Obj-C program, with the "complication" of inserting the current time argument (123.456 in the above code).

It looks like this:

NSString * jsTemplate =
    @"( function(time) {"
    @"        $(\".t_h\").each(function(i, obj) {"
    @"            if ($(this).text() != time)  return;"
    @"            $(this).parent().find(\"form\").each(function(i, obj) {"
    @"                obj.submit();"
    @"            });"
    @"        });"
    @"    })( %g );" ;
NSString * js = [ NSString stringWithFormat:jsTemplate, 123.456 ] ;
NSString * result = [ webView stringByEvaluatingJavaScriptFromString:js ] ;

I think I've written enough now :)

Your above example works, and result="success!" is printed in the console. However, when I use my own javascript instead of "success", blank quotation marks are printed in the console. Any ideas? — Conor Taylor, Sep 27 '12 at 09:01
If you want to run your function once, change your code to be `(function(){...})()` — nielsbot, Sep 27 '12 at 10:51
If you are going to use your function multiple times, use 2 steps. Assign your function to a variable (`submitFormForTime = function(time){...}`) then each time you want to execute your function do `submitFormForTime(...)`. — nielsbot, Sep 27 '12 at 10:53
You have to modify your code to do one of the above. My example is based on the two step version — nielsbot, Sep 27 '12 at 10:54
Wait, to have the function run only once, could you clarify it for me please? — Conor Taylor, Sep 27 '12 at 20:51

score 0 · Answer 2 · edited Sep 21 '12 at 18:12

I would get all the HTML from web view, then I'd inject the code and reload the page. It's still not a proper method of injection, but it may work.

NSString *htmlDataString = [webView stringByEvaluatingJavaScriptFromString: @"document.documentElement.outerHTML"];
// use nsstring methds to find the place for injecting
// inject avascript code
[webView loadHTMLString:htmlDataString baseURL:nil];

Of course you may have base URL from your request, if so replace that nil.

score 0 · Answer 3 · answered Sep 25 '12 at 20:12

I didn't tried this, but if the problem is with the brackets and the complexity of the code, you can try calling a JS file stored in the bundle. Maybe it solves that. For example:

NSData *fileData = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@”submitFormForTime” ofType:@”js”]];

NSString *jsString = [[NSMutableString alloc] initWithData:fileData encoding:NSUTF8StringEncoding];

[webView stringByEvaluatingJavaScriptFromString:jsString];

Maybe setting the encoding type helps to parse all the brackets in a right way.

Methods of JavaScript injection using Objective-C

3 Answers3