GWT JSNI return a js-function

Question

How can I return a JavaScript function from JSNI in GWT? I tried it the following way:

/* JSNI method returning a js-function */
public static native JavaScriptObject native_getFunction() /*-{
    return function(a,b){
        //do some stuff with a,b
    }
}-*/;

Store the function in a variable

/* outside from GWT: store the function in a variable */
JavaScriptObject myFunction = native_getFunction();

Using the function afterwards produces the following error message:

(TypeError): object is not a function

Does somebody know how to solve this problem?

The returned function is a d3.js transformation function which is used in several other JSNI methods to transform some data. To avoid redundancy and to dynamically change the transformation I would like to store it in a variable. — Michael
– Michael, Commented Feb 5, 2013 at 16:43
I don't understand why you cannot simply call this JS function from other JSNI methods, like you call any JS in your document, without storing it in a variable. — Andrei Volgin
– Andrei Volgin, Commented Feb 5, 2013 at 19:03
(1) why not call the function directly: as I said it is a transformation function from d3.js, but with custom parameters written by me. So whenever I would need the transformation function in any JSNI method I would have to write again the transformation function (duplicate code, maintainablility). (2) Therefore I define the function only once, store it in a variable and can then give this function as a parameter to any JSNI method which needs the transformation. — Michael
– Michael, Commented Feb 5, 2013 at 19:25
You can define your JS function, inject it in the document (using GWT ScriptInjector), and call it directly from any JSNI method. But I like Simon-Pierre's solution. — Andrei Volgin
– Andrei Volgin, Commented Feb 5, 2013 at 20:32

spg · Accepted Answer · 2013-02-05 18:38:01Z

6

This works for me. Declare these methods:

public static native JavaScriptObject native_getFunction() /*-{
    return function(a,b){
        //do some stuff with a,b
    }
}-*/;

private native void invoke(JavaScriptObject func)/*-{
    func("a", "b");
}-*/;

And then, you use these methods this way:

JavaScriptObject func = native_getFunction();
invoke(func);

answered Feb 5, 2013 at 18:38

spg

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Comments

Suresh Atta · Accepted Answer · 2013-02-05 19:01:43Z

0

Lets consider you appName.nochache.js(GWT) in Homepage.html

in homepage.html

<script>
    function printMyName(name) {
        alert("Hello from JavaScript, " + name);
    }
    </script>

In your Gwt :

Within your Gwt source, you can access the sayHello() JS function through JSNI:

native void printMyNameInGwt(String name) /*-{
  $wnd.printMyName(name); // $wnd is a JSNI synonym for 'window'
}-*/;

you can assign them to variables also

native void printMyNameInGwt(String name) /*-{
  var myname =$wnd.printMyName(name); // return that for your purposes
}-*/;

Note : if you are calling an js methods of any exterenal file that should be append on your html page with <script> tags...

answered Feb 5, 2013 at 19:01

Suresh Atta

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1 Comment

Michael Over a year ago

I think extracting the relevant methods to the html page would also be a nice solution. Thanks.

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