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Using Closure Compiler on ES6 Modules with Properties

So after a day of testing I'm almost there: using google-closure-compiler-js and gulp.js to minify / compile my ES6 module based "library".
There is just one problem left. How to call the properties of an imported module?
My test case consists of 3 files:
gulpfile.js
const gulp = require("gulp");
const compiler = require("google-closure-compiler-js").gulp();
const sourcemaps = require("gulp-sourcemaps");
gulp.task("default", function() {
// wildcards don't seem to work yet with the js version
// files need to be in reverse order of dependency...
return gulp.src(["src/boilerplate/main.js", "src/app.js"])
.pipe(sourcemaps.init())
.pipe(compiler({
jsOutputFile: "app.min.js",
compilationLevel: "ADVANCED",
warningLevel: "VERBOSE",
createSourceMap: true
}))
.pipe(sourcemaps.write("/"))
.pipe(gulp.dest("./dist"));
});
src/boilerplate/main.js
var mod = {};
export default mod;
var foo = "FOO";
var bar = "BAR";
function foobar(join) {
join = (typeof join === "string") ? join : "";
return foo + join + bar;
}
Object.defineProperty(mod, "foobar", {value: foobar});
src/app.js
import boilerplate from "./boilerplate/main.js";
console.log(boilerplate["foobar"]("+"));
console.log(boilerplate.foobar("+"));
If you log boilerplate here, you see that it has the property "foobar". Symbol intact and all. Great!
Hence app.js' first call – bracket notation ["foobar"] – works perfectly fine. However, the dot notation does not. Calls to an imported module's property get minified by Closure Compiler!
You get your classic "Hi. I'm new to ADVANCED mode" error: TypeError: a.a is not a function.
How do I prevent this? (& let's assume exporting foobar directly isn't viable, for real world's sake.)
Do I need an exports file? How exactly would I do that? My first ventures in that direction did not take me far... is there a trick specific to google-closure-compiler-js?
Is there some kind of hack that allows for dot notation, until Closure Compiler adds a feature that automatically does not rename calls to properties of imports?
And what does this closure-compiler/wiki's article about JS-Modules#type-references advise me to do? Is this the answer I fail to implement?
/** #param {foo.Foo} Foo */
function(Foo) {}

For ADVANCED mode compatibility, use Object.defineProperties to avoid quoted strings.
Object.defineProperties(mod, {
foobar: {value: foobar}
});
Anytime you use quoted strings, you will be required to use brackets (or other techniques) or risk violating the consistent property access rules.

javascript: prototype in javascript like reflection in c#, is it possible? [duplicate]

In Ruby I think you can call a method that hasn't been defined and yet capture the name of the method called and do processing of this method at runtime.
Can Javascript do the same kind of thing ?

method_missing does not fit well with JavaScript for the same reason it does not exist in Python: in both languages, methods are just attributes that happen to be functions; and objects often have public attributes that are not callable. Contrast with Ruby, where the public interface of an object is 100% methods.
What is needed in JavaScript is a hook to catch access to missing attributes, whether they are methods or not. Python has it: see the __getattr__ special method.
The __noSuchMethod__ proposal by Mozilla introduced yet another inconsistency in a language riddled with them.
The way forward for JavaScript is the Proxy mechanism (also in ECMAscript Harmony), which is closer to the Python protocol for customizing attribute access than to Ruby's method_missing.

The ruby feature that you are explaining is called "method_missing" http://rubylearning.com/satishtalim/ruby_method_missing.htm.
It's a brand new feature that is present only in some browsers like Firefox (in the spider monkey Javascript engine). In SpiderMonkey it's called "__noSuchMethod__" https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/NoSuchMethod
Please read this article from Yehuda Katz http://yehudakatz.com/2008/08/18/method_missing-in-javascript/ for more details about the upcoming implementation.

Not at the moment, no. There is a proposal for ECMAScript Harmony, called proxies, which implements a similar (actually, much more powerful) feature, but ECMAScript Harmony isn't out yet and probably won't be for a couple of years.

You can use the Proxy class.
var myObj = {
someAttr: 'foo'
};
var p = new Proxy(myObj, {
get: function (target, methodOrAttributeName) {
// target is the first argument passed into new Proxy, aka. target is myObj
// First give the target a chance to handle it
if (Object.keys(target).indexOf(methodOrAttributeName) !== -1) {
return target[methodOrAttributeName];
}
// If the target did not have the method/attribute return whatever we want
// Explicitly handle certain cases
if (methodOrAttributeName === 'specialPants') {
return 'trousers';
}
// return our generic method_missing function
return function () {
// Use the special "arguments" object to access a variable number arguments
return 'For show, myObj.someAttr="' + target.someAttr + '" and "'
+ methodOrAttributeName + '" called with: ['
+ Array.prototype.slice.call(arguments).join(',') + ']';
}
}
});
console.log(p.specialPants);
// outputs: trousers
console.log(p.unknownMethod('hi', 'bye', 'ok'));
// outputs:
// For show, myObj.someAttr="foo" and "unknownMethod" called with: [hi,bye,ok]
About
You would use p in place of myObj.
You should be careful with get because it intercepts all attribute requests of p. So, p.specialPants() would result in an error because specialPants returns a string and not a function.
What's really going on with unknownMethod is equivalent to the following:
var unk = p.unkownMethod;
unk('hi', 'bye', 'ok');
This works because functions are objects in javascript.
Bonus
If you know the number of arguments you expect, you can declare them as normal in the returned function.
eg:
...
get: function (target, name) {
return function(expectedArg1, expectedArg2) {
...

I've created a library for javascript that let you use method_missing in javascript: https://github.com/ramadis/unmiss
It uses ES6 Proxies to work. Here is an example using ES6 Class inheritance. However you can also use decorators to achieve the same results.
import { MethodMissingClass } from 'unmiss'
class Example extends MethodMissingClass {
methodMissing(name, ...args) {
console.log(`Method ${name} was called with arguments: ${args.join(' ')}`);
}
}
const instance = new Example;
instance.what('is', 'this');
> Method what was called with arguments: is this

No, there is no metaprogramming capability in javascript directly analogous to ruby's method_missing hook. The interpreter simply raises an Error which the calling code can catch but cannot be detected by the object being accessed. There are some answers here about defining functions at run time, but that's not the same thing. You can do lots of metaprogramming, changing specific instances of objects, defining functions, doing functional things like memoizing and decorators. But there's no dynamic metaprogramming of missing functions as there is in ruby or python.

I came to this question because I was looking for a way to fall through to another object if the method wasn't present on the first object. It's not quite as flexible as what your asking - for instance if a method is missing from both then it will fail.
I was thinking of doing this for a little library I've got that helps configure extjs objects in a way that also makes them more testable. I had seperate calls to actually get hold of the objects for interaction and thought this might be a nice way of sticking those calls together by effectively returning an augmented type
I can think of two ways of doing this:
Prototypes
You can do this using prototypes - as stuff falls through to the prototype if it isn't on the actual object. It seems like this wouldn't work if the set of functions you want drop through to use the this keyword - obviously your object wont know or care about stuff that the other one knows about.
If its all your own code and you aren't using this and constructors ... which is a good idea for lots of reasons then you can do it like this:
var makeHorse = function () {
var neigh = "neigh";
return {
doTheNoise: function () {
return neigh + " is all im saying"
},
setNeigh: function (newNoise) {
neigh = newNoise;
}
}
};
var createSomething = function (fallThrough) {
var constructor = function () {};
constructor.prototype = fallThrough;
var instance = new constructor();
instance.someMethod = function () {
console.log("aaaaa");
};
instance.callTheOther = function () {
var theNoise = instance.doTheNoise();
console.log(theNoise);
};
return instance;
};
var firstHorse = makeHorse();
var secondHorse = makeHorse();
secondHorse.setNeigh("mooo");
var firstWrapper = createSomething(firstHorse);
var secondWrapper = createSomething(secondHorse);
var nothingWrapper = createSomething();
firstWrapper.someMethod();
firstWrapper.callTheOther();
console.log(firstWrapper.doTheNoise());
secondWrapper.someMethod();
secondWrapper.callTheOther();
console.log(secondWrapper.doTheNoise());
nothingWrapper.someMethod();
//this call fails as we dont have this method on the fall through object (which is undefined)
console.log(nothingWrapper.doTheNoise());
This doesn't work for my use case as the extjs guys have not only mistakenly used 'this' they've also built a whole crazy classical inheritance type system on the principal of using prototypes and 'this'.
This is actually the first time I've used prototypes/constructors and I was slightly baffled that you can't just set the prototype - you also have to use a constructor. There is a magic field in objects (at least in firefox) call __proto which is basically the real prototype. it seems the actual prototype field is only used at construction time... how confusing!
Copying methods
This method is probably more expensive but seems more elegant to me and will also work on code that is using this (eg so you can use it to wrap library objects). It will also work on stuff written using the functional/closure style aswell - I've just illustrated it with this/constructors to show it works with stuff like that.
Here's the mods:
//this is now a constructor
var MakeHorse = function () {
this.neigh = "neigh";
};
MakeHorse.prototype.doTheNoise = function () {
return this.neigh + " is all im saying"
};
MakeHorse.prototype.setNeigh = function (newNoise) {
this.neigh = newNoise;
};
var createSomething = function (fallThrough) {
var instance = {
someMethod : function () {
console.log("aaaaa");
},
callTheOther : function () {
//note this has had to change to directly call the fallThrough object
var theNoise = fallThrough.doTheNoise();
console.log(theNoise);
}
};
//copy stuff over but not if it already exists
for (var propertyName in fallThrough)
if (!instance.hasOwnProperty(propertyName))
instance[propertyName] = fallThrough[propertyName];
return instance;
};
var firstHorse = new MakeHorse();
var secondHorse = new MakeHorse();
secondHorse.setNeigh("mooo");
var firstWrapper = createSomething(firstHorse);
var secondWrapper = createSomething(secondHorse);
var nothingWrapper = createSomething();
firstWrapper.someMethod();
firstWrapper.callTheOther();
console.log(firstWrapper.doTheNoise());
secondWrapper.someMethod();
secondWrapper.callTheOther();
console.log(secondWrapper.doTheNoise());
nothingWrapper.someMethod();
//this call fails as we dont have this method on the fall through object (which is undefined)
console.log(nothingWrapper.doTheNoise());
I was actually anticipating having to use bind in there somewhere but it appears not to be necessary.

Not to my knowledge, but you can simulate it by initializing the function to null at first and then replacing the implementation later.
var foo = null;
var bar = function() { alert(foo()); } // Appear to use foo before definition
// ...
foo = function() { return "ABC"; } /* Define the function */
bar(); /* Alert box pops up with "ABC" */
This trick is similar to a C# trick for implementing recursive lambdas, as described here.
The only downside is that if you do use foo before it's defined, you'll get an error for trying to call null as though it were a function, rather than a more descriptive error message. But you would expect to get some error message for using a function before it's defined.

Javascript: How to get the parent key inside a function?

I've some functions, stored in a collection/array and would like to get the key (function-name) without retyping it. Is there any short way to access it?
var functions_collection = {
"function_x": function() {
var name = "function_x";
// name = this.key; <- how to get the key/function-name "function_x"?
// some more code like:
$(".function_x .button").val();
alert(name);
}
}
Edit: I'd like to avoid retyping the "function_x" inside the function itself and prefer to call it like this.key.
Sorry for the weird topic and thanks in advance!
Solution: A lot of good answers, but I was just looking for this snipped:
Object.keys(this)

I'm not sure it's what you want but you can do this :
var functions_collection = {};
(function(name){
functions_collection[name] = function(){
// use name, which is the function
alert(name);
};
})("function_x");
I'm not really sure it's better. But depending on your (unspecified) goal, there's probably a better solution.

To get the name of the objects keys, you can use Object.getOwnPropertyNames(this) or in newer browsers just Object.keys(this), and that will get you an array of all and any keys the this object has :
var functions_collection = {
function_x: function() {
var name = Object.keys(this);
console.log(name);
}
}
FIDDLE

In my opinion you´d need to change you above code since you are having anonymous functions which have no name - a change like this should work:
var functions_collection = {
'function_x' : function function_x () {
var myName = arguments.callee.name;
alert(myName);
}
}
see http://jsfiddle.net/9cN5q/1/

There are several ways you could go here. Some are good ideas, some are not.
First, some bad ideas
Bad idea: arguments.callee.name
This translates most directly to what you ask. arguments.callee is
a reference to the function you're currently in. However, it's
considered bad
practice,
and you should avoid using it unless you have a really good reason.
Bad idea: Currying
After constructing the function, bind its own name into it as a parameter:
var functions_collection = {
"function_x": function(name) {
alert(name);
},
//more functions
};
for (var name in functions_collection) {
if (typeof functions_collection[name] === "function") {
functions_collection[name] =
functions_collection[name].bind(functions_collection, name);
}
}
Currying is useful for lots of things in JavaScript, and it's a great idea in many situations. Not here, though, and I'll explain why below.
Bad idea: Use a local parameter and iterate through the containing object
var functions_collection = {
"function_x": function(name) {
alert(name);
},
//more functions
};
for (var name in functions_collection) {
if (typeof functions_collection[name] === "function") {
functions_collection[name](name);
}
}
Of course, the obvious problem with this one is that you might not want to call every function in the collection at once. The more fundamental problem is that it continues the trend of dangerously tight coupling. This is a bad thing, potentially a Very Bad Thing that will cost you all kinds of headaches down the line.
Now the "right" way
Change your whole approach. Forget trying to recycle class names from your HTML; just keep it simple.
Good idea: Use a local variable
Who cares what you name your functions? If you know which HTML classes you want them to touch, just code them that way.
var functions_collection = {
"function_x": function() {
var name = "function_x"; //or "button" or any other class name
alert(name);
},
//more functions
};
functions_collection.function_x();
Good idea: Pass a parameter
You're already calling the function, right? So there's probably already code somewhere with access to the name you want.
var functions_collection = {
"function_x": function(name) {
alert(name);
},
//more functions
};
functions_collection.function_x("function_x"); //or any other class name
Now you can use function_x on any class in your HTML, even if it doesn't match the function name:
functions_collection.function_x("function_y");
functions_collection.function_x("class_z");
functions_collection.function_x("button");
I've saved the simplest for last because I think you're making a mistake by trying to be "clever", if that makes sense. There are significant risks in your approach, and the payoff isn't going to be worth it.
Why the bad ideas are bad and the good ideas are good
Other than the arguments.callee.name option, the reason 2 and 3 are bad in this case is tight coupling. You're coupling function_x to the structure of functions_collection; you're coupling behavior to a variable name; and worst of all, you're coupling JS variables to the class names of HTML elements. This will make your code extremely fragile, and when you want to change something (and you will), get ready for a world of hurt.
For example, what happens if you reorganize your HTML? The page probably breaks, since the structure of your JS has to match the classes in your HTML/CSS. You'll have to rename or rewrite functions_collection and all others like it, or else you'll have to carefully plan new HTML around the JS you already have.
What happens if you want to use a JS minifier? Depends, but if you allow it to change member names in object literals, it completely breaks everything and you have to start over with one of the "good" ideas.
Now, what do you get in exchange for this inflexibility? You save an extra line at the beginning of each function. Not worth it, IMHO. Just bite the bullet and keep it simple.

Supposing that the variable name has the same name as its containing function:
var keys = [];
for (var p in functions_collection) {
if (typeof(functions_collection[p]) == 'function') {
keys.push(p);
}
}
And there you have it, an array with all the function names.

Get name of prototype object

This question just got upvoted so can update question with what I did
I solved it by iterating over the window object (or user specified object root) and when I found the correct instance I backtracked and got the name from the index. The final solution can be found here
https://github.com/AndersMalmgren/Knockout.BindingConventions
Update end
I'm planning on writing a convention over configuration template source engine for KnockoutJS / MVC.
I'm started with a little client side POC and ran into a show stopper right away
My plan is use this syntax or something similar
MyApp.EditCustomersViewModel = function() {
ko.templates.loadView(this);
};
When doing this it will check the tamplate cache or fetch the templates from server using the object name as key.
The problem is I cant get the name of the prototype object, i tried this
Object.prototype.getName = function() {
var funcNameRegex = /function (.{1,})\(/;
var results = (funcNameRegex).exec((this).constructor.toString());
return (results && results.length > 1) ? results[1] : "";
};
If works for objects defined like this
function MyClass() {
}
If you add a prototype to the above object it will not work, or if you define it like this
MyApp = {};
MyApp.MyClass = function() {
};
Prototype and scoping is two musts so this is a showstopper, any ideas?
Fiddle: http://jsfiddle.net/aRWLA/
edit: The background for this is like this.
On the server you have structure like this
Templates\ [ViewName]\index.html
Templates\ [ViewName]\sub-model-template.html
on the client you will do
MyApp.EditCustomersViewModel = function() {
ko.templates.loadView(this);
};
which will generate a ajax request with the objects name as key, which will fetch all the templates for the view in question

Only hoisted functions (function someFunc() {) have a retrievable name.
Assigned functions do not, because you are not technically naming the function but creating an anonymous function and assigning a reference to it (in the memory) to a named variable.
So it's the var, not the function, that is named.
This makes the very idea of retrieving function names pretty much a none-starter, since in any vaguely mature pattern you'll be writing methods, not hoisted functions - and methods of course are assigned functions.
Named expressions (see other answers) are a partial workaround but these have other issues - not least lack of support in older IEs.
(Sidenote: I've long expected browser vendors to build around this such that the names of assigned functions became retrievable, but no joy yet AFAIK.)

I think you problem in improper replacing function prototype: if you replace function prototype object then you must preserve constructor member in prototype:
function Test1() {
}
Test1.prototype={
constructor: Test1
};
MyApp={};
MyApp.MyClass=function MyClass(){
};
MyApp.MyClass.prototype={
constructor: MyApp.MyClass
};
Your example: http://jsfiddle.net/aRWLA/1/
Modified example: http://jsfiddle.net/aRWLA/2/

You can make use of named function expressions:
MyApp.MyClass = function MyClass() { ... };
But note that (suprise) they don't work correctly in all versions of IE.
See: http://kangax.github.com/nfe/

THIS DOES NOT ANSWER THE QUESTION
However, the code might be useful to other people, so I'm leaving it here, just in case. I don't expect upvotes, but please don't abuse it for downvoting either. Thanks.
I don't know your use case, as such I think you've got a design issue - the problem you describe shouldn't happen in practice.
But let's say you do need to have this working. An easy way to do what you need would be something like:
function findNamed(obj, fn){
for(var p in obj)
if(obj[p] === fn)
return p;
return false;
}
var m = {};
m.MyClass = function() {};
console.log(findNamed(m, m.MyClass));
Of course, the solution could be made into a more appropriate OOP form, but this is just to give an idea.
To replicate your use case, it would look like:
m.MyClass = function() {
findNamed(this, arguments.callee);
};
So, the final code is:
Object.prototype.getNameOfCall = function(fn) {
for(var p in this)
if(this[p] === fn)
return p;
throw "Callback not in object.";
};
var m = {};
m.MyClass = function() {
console.log(this.getNameOfCall(arguments.callee)); // MyClass
};
m.MyClass(); // test it out

JS: using eval on a function while trying to pass an array as parameter, but it throws an error

i want to create a dynamic generated form using javascript, everything works fine, until i try to pass an array as parameter. When i do this, an error happens. Coulr anyone explain what this is?
Heres my code:
var loadFrm = function(component) {
for(nItem in component) {
var myComponent = "add" + firstToUpper(component[nItem].type);
var callComponent = myComponent + "(" + component[nItem].opt + ");";
eval(callComponent);
}
}
var json = [
{
type: "scale",
opt: {content: [{label: "male", value: "m"}, {label: "female", value: "f"}]}
}
];
loadFrm(json);
Edit Here's the error:
missing ] after element list
[Break on this error] addScale([object Object]);

If you use a debugger to look at the string callComponent, you'll probably find it looks something like this:
addScale([object Object])
...which isn't what you want. That's because you're effectively calling toString on your opt object, and the default toString on objects just looks like that. The eval error is because that's invalid syntax.
Generally speaking, any time you think you need to use eval, there's almost certainly a better answer. In this case, it looks like you're trying to call a function and pass in opt. Assuming these functions are "globals", you can do that like this:
var loadFrm = function(component) {
var nItem, functionName;
for (nItem = 0; nItem < component.length; ++nItem) {
functionName = "add" + firstToUpper(component[nItem].type);
window[functionName](component[nItem].opt);
}
}
Live example
Notes on the above:
Don't use for..in to loop through arrays unless you really know what you're doing. for..in does not enumerate the indexes of an array, it enumerates the properties of an object.
We look up the function by name using window[functionName]. This works because "globals" are actually properties of the window object, and you can look up properties using a string name for them using bracketed notation.
Having gotten the function via window[functionName], we just call it directly, passing in the object opt rather than a string form of it. I assume addScale expects to see an object.
I moved all of the vars to the top of the function because that's where they really are (details).
If you can, I'd recommend moving addScale and the related functions to their own object rather than putting them on window. The window namespace is already pretty crowded. Here's the live example modified to not add any symbols to window at all, instead putting the addScale function on an object called functions and using it from there.
Off-topic: The syntax var loadFrm = function(component) creates an anonymous function that it then assigns to a variable. This is used a lot, but unless you're creating different functions based on a condition, e.g.:
var f;
if (...) {
f = function() { ... };
}
else {
f = function() { ... };
}
...it's not actually useful. (If you are creating different functions based on a condition like that, then it's not only useful, it's necessary.) I recommend using named functions whenever possible, because a function with a name helps your tools help you by showing you the function name in error messages, call stacks, etc.
Off-topic 2: You have a variable called json, but FYI, it's not using JSON notation. It's using a combination of JavaScript array and object literal notation, which is a superset of JSON. You'll see a lot of people confused about this, I mention it because you said you're new and so it's worth nipping in the bud. :-) JSON is purely a notation. (A very useful one.)

Use this:
fn = eval(functionName);
fn(objParameter)