Thanks for the explanation and examples. I actually know javascript quite well, including the ramifications of using this inside of closures, but as I said, I didn't know that $entry was setting up a closure.
You've given me enough information that I believe I can figure out my problems now. Thanks for helping me out! On Sat, Feb 15, 2014 at 9:26 AM, Thomas Broyer <[email protected]> wrote: > > > On Saturday, February 15, 2014 6:00:47 PM UTC+1, rjcarr wrote: >> >> Thanks for the quick responses. That makes sense that since the jsni >> method is declared static that you can't use this, but I'm not following >> Thomas's explanation. Maybe I could just get an explanation from the docs >> example here: >> >> http://www.gwtproject.org/doc/latest/DevGuideCodingBasicsJSNI.html# >> methods-fields >> >> Under the example: Accessing Java fields from JavaScript >> >> Where it has: >> >> public class JSNIExample { >> >> String myInstanceField; >> static int myStaticField; >> >> void instanceFoo(String s) { >> // use s >> } >> >> static void staticFoo(String s) { >> // use s >> } >> >> public native void bar(JSNIExample x, String s) /*-{ >> // Call instance method instanceFoo() on this >> >> [email protected]::instanceFoo(Ljava/lang/String;)(s); >> >> // Call instance method instanceFoo() on x >> >> [email protected]::instanceFoo(Ljava/lang/String;)(s); >> >> // Call static method staticFoo() >> @com.google.gwt.examples.JSNIExample::staticFoo(Ljava/lang/String;)(s); >> >> What's the difference here between using the 'this' and the passed in >> 'x'? What does 'this' represent in this example? >> > > The 'this' is the same here as it would be in Java, difference between > 'this' and 'x' is the same too. > > >> >> As for Thomas's explanation, are you saying that by calling $entry it >> creates a new inner function (or closure) where 'this' is no longer what it >> was? So if I didn't use $entry then 'this' would be what I expect it is? >> > > It has nothing to do with $entry() but the fact that you export a method > of an object, and the way things (and specifically 'this') work in > JavaScript. > > Let's use pure JS: > > function JSExample() { }; > JSExample.prototype.instanceFoo = function(s) { > // use s > }; > JSExample.staticFoo = function(s) { > // use s > }; > JSExample.prototype.bar = function(x, s) { > this.instanceFoo(s); > x.instanceFoo(s); > JSExample.staticFoo(s); > }; > > We can create a JSExample instance and call bar: > > var y = new JSExample(); > y.bar(new JSExample(), "msg"); > > Now export the method from 'y' without binding it to the JSExample > instance and try to call it: > > var foo = y.bar; // could be window.foo instead of var foo; y.bar is the > same as JSExample.prototype.bar > foo(new JSExample(), "msg"); // fails because 'window' (the current > 'this') does not have an 'instanceFoo' property > foo.call(y, new JSExample(), "msg"); // works because we explicitly set > the 'this' to 'y' > > Now export the method, binding it to 'y' (using a closure) and call it: > > var foo = function(x, s) { y.bar(x, s); }; > foo(new JSExample(), "msg"); // works, because we call 'bar' on 'y' > > Introduce $entry: > > var foo = $entry(function(x, s) { y.bar(x, s); }); > foo(new JSExample(), "msg"); // works the same > > With ECMAScript 5, you could now use y.bar.bind(y) instead of using a > closure, and with "use strict" the "default 'this'" would be 'null', not > 'window'. > > When I say GWT doesn't free you from knowing JS, I really mean it! > > -- > You received this message because you are subscribed to a topic in the > Google Groups "Google Web Toolkit" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/google-web-toolkit/rJAnzDPb_2Y/unsubscribe > . > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/google-web-toolkit. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "Google Web Toolkit" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-web-toolkit. For more options, visit https://groups.google.com/groups/opt_out.
