How is it possible to learn the name of function I am in?
The below code alerts 'Object'. But I need to know how to alert "Outer."
function Outer(){
alert(typeof this);
}
This will work:
function test() {
var z = arguments.callee.name;
console.log(z);
}
I think that you can do that :
var name = arguments.callee.toString();
For more information on this, take a look at this article.
function callTaker(a,b,c,d,e){
// arguments properties
console.log(arguments);
console.log(arguments.length);
console.log(arguments.callee);
console.log(arguments[1]);
// Function properties
console.log(callTaker.length);
console.log(callTaker.caller);
console.log(arguments.callee.caller);
console.log(arguments.callee.caller.caller);
console.log(callTaker.name);
console.log(callTaker.constructor);
}
function callMaker(){
callTaker("foo","bar",this,document);
}
function init(){
callMaker();
}
As of ES6, you can use Function.prototype.name. This has the added benefit of working with arrow functions, since they do not have their own arguments object.
function logFuncName() {
console.log(logFuncName.name);
}
const logFuncName2 = () => {
console.log(logFuncName2.name);
};
Took me a while to figure this out, so tried to make it very clear for rookies like me.
Approach 1 - arguments.callee.name
This approach used to work, but now in ES6 Strict Mode it will fail. Don't use Approach 1.
//approach 1 - don't use
let functionName = arguments.callee.name;
console.log(functionName);
Approach 2 - create a function and use caller.name
This approach works in the latest version of Javascript and will not fail in Strict Mode. Use Approach 2. There are 2 steps.
Step 1 - Create a function that uses caller.name to return the name of the function that called it. Add this function to your code:
function getFuncName() {
return getFuncName.caller.name
}
Step 2 - Call your function when you need the name of the function your code is currently in.
function iWantThisName() {
console.log(getFuncName())
}
iWantThisName()
// Logs: "iWantThisName"
Related
Here is a simplified snippet from some code I wrote for managing tablet gestures on canvas elements
first a function that accepts an element and a dictionary of callbacks and register the events plus adding other features like 'hold' gestures:
function registerStageGestures(stage, callbacks, recieverArg) {
stage.inhold = false;
stage.timer = null;
var touchduration = 1000;
var reciever = recieverArg || window;
stage.onLongTouch = function(e) {
if (stage.timer) clearTimeout(stage.timer);
stage.inhold = true;
if (callbacks.touchholdstart) callbacks.touchholdstart.call(reciever, e);
};
stage.getContent().addEventListener('touchstart', function(e) {
e.preventDefault();
calcTouchEventData(e);
stage.timer = setTimeout(function() {
stage.onLongTouch(e);
}, touchduration);
if (callbacks.touchstart) callbacks.touchholdstart.call(reciever, e);
});
stage.getContent().addEventListener('touchmove', function(e) {
e.preventDefault();
if (stage.timer) clearTimeout(stage.timer);
if (stage.inhold) {
if (callbacks.touchholdmove) callbacks.touchholdmove.call(reciever, e);
} else {
if (callbacks.touchmove) callbacks.touchmove.call(reciever, e);
}
});
stage.getContent().addEventListener('touchend', function(e) {
e.preventDefault();
if (stage.timer) clearTimeout(stage.timer);
if (stage.inhold) {
if (callbacks.touchholdend) callbacks.touchholdend.call(reciever, e);
} else {
if (callbacks.touchend) callbacks.touchend.call(reciever, e);
}
stage.inhold = false;
});
}
later I call registerStageGestures on a few elements (represented by 'View' objects) in the same page. Something like:
function View() {
var self=this;
..
function InitView() {
...
registerStageGestures(kineticStage, {
touchstart: function(e) {
// do something
},
touchmove: function(e) {
// do something
},
touchendunction(e) {
// do something
},
touchholdstart: function(e) {
// do something
},
touchholdmove: function(e) {
// do something
},
touchholdend: function(e) {
// do something
},
}, self);
Everything works fine, however I'm left wondering about two things in the implementation of registerStageGestures:
First, is it necessary to make inhold, timer and onLongTouch members of the stage ? or will closures make everything works well if they are local vars in registerStageGestures ?
Second, is it necessary to call the callbacks with '.call(receiver,' syntax ? I'm doing this to make sure the callback code will run in the context of the View but I'm not sure if it's needed ?
any input is much appreciated
Thanks!
First, is it necessary to make inhold, timer and onLongTouch members
of the stage ? or will closures make everything works well if they are
local vars in registerStageGestures ?
As far as registerStageGestures() is concerned, var inhold, var timer and function onLongTouch(e) {...}. would suffice. The mechanism by which an inner function has automatic access to its outer function's members is known as "closure". You would only need to set stage.inhold, stage.timer and stage.onLongTouch if some other piece of code needs access to these settings as properties of stage.
Second, is it necessary to call the callbacks with '.call(receiver,'
syntax ? I'm doing this to make sure the callback code will run in the
context of the View but I'm not sure if it's needed ?
Possibly, depending on how those callbacks are written. .call() and .apply() are sometimes used when calling functions that use this internally. In both cases, the first parameter passed defines the object to be interpreted as this. Thus, javascript gives you the means of defining general purpose methods with no a priori assumption about the object to which those methods will apply when called. Similarly, you can call a method of an object in such a way that it acts on another object.
EDIT:
For completeness, please note that even in the absence of this in a function, .apply() can be very useful as it allows multiple parameters to be specified as elements of a single array, eg the ubiquitous jQuery.when.apply(null, arrayOfPromises)...
There are some simple answers, here.
First, closure:
Closure basically says that whatever is defined inside of a function, has access to the rest of that function's contents.
And all of those contents are guaranteed to stay alive (out of the trash), until there are no more objects left, which ere created inside.
A simple test:
var testClosure = function () {
var name = "Bob",
recallName = function () { return name; };
return { getName : recallName };
};
var test = testClosure();
console.log(test.getName()); // Bob
So anything that was created inside can be accessed by any function which was also created inside (or created inside of a function created in a function[, ...], inside).
var closure_2x = function () {
var name = "Bob",
innerScope = function () {
console.log(name);
return function () {
console.log("Still " + name);
}
};
return innerScope;
};
var inner_func = closure_2x();
var even_deeper = inner_func(); // "Bob"
even_deeper(); // "Still Bob"
This applies not only to variables/objects/functions created inside, but also to function arguments passed inside.
The arguments have no access to the inner-workings(unless passed to methods/callbacks), but the inner-workings will remember the arguments.
So as long as your functions are being created in the same scope as your values (or a child-scope), there's access.
.call is trickier.
You know what it does (replaces this inside of the function with the object you pass it)...
...but why and when, in this case are harder.
var Person = function (name, age) {
this.age = age;
this.getAge = function () {
return this.age;
};
};
var bob = new Person("Bob", 32);
This looks pretty normal.
Honestly, this could look a lot like Java or C# with a couple of tweaks.
bob.getAge(); // 32
Works like Java or C#, too.
doSomething.then(bob.getAge);
? Buh ?
We've now passed Bob's method into a function, as a function, all by itself.
var doug = { age : 28 };
doug.getAge = bob.getAge;
Now we've given doug a reference to directly use bobs methid -- not a copy, but a pointer to the actual method.
doug.getAge(); // 28
Well, that's odd.
What about what came out of passing it in as a callback?
var test = bob.getAge;
test(); // undefined
The reason for this, is, as you said, about context...
But the specific reason is because this inside of a function in JS isn't pre-compiled, or stored...
this is worked out on the fly, every time the function is called.
If you call
obj.method();
this === obj;
If you call
a.b.c.d();
this === a.b.c;
If you call
var test = bob.getAge;
test();
...?
this is equal to window.
In "strict mode" this doesn't happen (you get errors really quickly).
test.call(bob); //32
Balance restored!
Mostly...
There are still a few catches.
var outerScope = function () {
console.log(this.age);
var inner = function () {
console.log("Still " + this.age);
};
inner();
};
outerScope.call(bob);
// "32"
// "Still undefined"
This makes sense, when you think about it...
We know that if a function figures out this at the moment it's called -- scope has nothing to do with it...
...and we didn't add inner to an object...
this.inner = inner;
this.inner();
would have worked just fine (but now you just messed with an external object)...
So inner saw this as window.
The solution would either be to use .call, or .apply, or to use function-scoping and/or closure
var person = this,
inner = function () { console.log(person.age); };
The rabbit hole goes deeper, but my phone is dying...
My question is simple:
I'm passing a function to some other function to be call later (sample callback function), the question is when, why and what is the best practice to do it.
Sample:
I have the xxx() function, and I have to pass it, as I show you below in the window.onload event.
What is the best practice and why? There is any performance aspect or why should I choose to use call or bind to call this function
function xxx(text)
{
var div = document.createElement("div");
div.innerHTML = text + " - this: " + this.toString();
document.body.appendChild(div)
}
function callFunction(func)
{
func("callFunction");
}
function callUsingCall(func)
{
func.call(this, ["callUsingCall"]);
}
function callUsingBind(func)
{
func.call(this, ["callUsingCall"]);
}
window.onload = function(){
callFunction(xxx);
callUsingCall(xxx);
callUsingBind(xxx.bind(document));
}
Thank you,
Sebastian P.
I don't think there's any "best" practise.
You use call if the function you're calling cares what this is.
You use bind if you want to ensure that the function can only be called with the specified value of this.
[There's some overhead to both, i.e. at least one depth of function calls / scope]
Otherwise you just call the function.
Simples :)
The this object is the context of the function. It's like you make a machine that something for you, and the this object would be the place that the machine works in, like your house. You can move it as you like.
We have 4 ways setting this objects.
Calling the function that is not a method:
fn(someArguments)
This way the this object is set to null or probably the window object.
Calling the function as a method:
someObject.fn(someArguments)
In this case the this object will point to someObject and it's mutable.
Calling with call or apply methods of the function.
fn.call(anotherObject, someArguments)
someObject.call(anotherObject, someArguments)
someObject.apply(anotherObject, [someArguments])
In this case the this object will point to someObject here. You are forcing it to have another context, when calling it.
Binding a the function
var fn2 = fn.bind(anotherObject, someArguments)
This will create another function that is binded to that this object we gave it(anotherObject). No matter how you call it, the this object is going to be the same.
Use Cases
Now you can do some tricky stuff knowing this. The reason that why we have it here(I think it came first from C++) is that methods of an object need to access to their parent. The this object provides the access.
var coolObject = {
points : ['People are amazing'],
addPoint : function (p) { this.points.push(p) }
}
So if you do the following it won't work:
var addPoint = coolObject.addPoint;
addPoint('This will result in an error');
The error will be thrown because the this object is not our coolObject anymore and doesn't have the points property. So at times like this, you can something like this:
var addPoint = coolObject.addPoint;
addPoint.call({points : []}, 'This is pointless');
This is pointless, but the function will work, even the this object is not what its supposed to be.
var anotherCoolObject = {
points : ['Im a thief!'],
addPoint : coolObject.addPoint
}
anotherCoolObject.addPoint('THIS IS CALL STEALING');
Still the function will work if you call it like that, since the this object will point to anotherCoolObject which has the points property.
The most popular use case I've seen is slicing the arguments object:
function returnHalf() {
return [].slice.call(arguments, 0, arguments.length / 2);
}
returnHalf('Half', 'is', 'not', 'awesome');
// >> [Half', 'is']
So you see, arguments object is not an instanceof array. If we do arguments.slice(...) then you're gonna be killed by the compiler. But here we use the array's method on arguments object, since it's array like.
Sometimes you don't want your function context to be changed or you wanna add your own arguments, you use bind.
For example when you add a listener for an event with jquery, when jquery calls your function, the this object will be the element. But sometimes you wanna do tricky stuff and change it:
var myElement = {
init : function () {
$(this.element).click(this.listener.bind(this));
},
view : "<li>${Name}</li>",
name : 'ed',
element : $('#myelement'),
listener : function () {
this.element.append($.tmpl( this.view, this ));
}
}
myElement.init();
So here, you bind it to the myElement, so you can have access to the object properties to render the view. Another examples would be the following:
for (var i = 0; i < 10; i++) {
setTimeout(function () {console.log(i)}, 10)
}
// All of them will be 10.
for (var i = 0; i < 10; i++) {
setTimeout((function () {console.log(this.i)}).bind({ i : i }, 10)
}
If you have put an asynchronous function call in a loop, by the time the callback is called, the loop is finished, and the counter have reached the end, you can use bind to cleanly bind the current counter to your callback.
Another good use case of it, that I use a lot is when passing my functions with arguments to async module, without creating closures.
async.parallel({
writeFile : function (cb) {
fs.writeFile('lolz.txt', someData, cb);
},
writeFile2 : function (cb) {
fs.writeFile('lolz2.txt', someData, cb);
}
}, function (err){
console.log('finished')
});
async.parallel({
writeFile : fs.writeFile.bind(fs, 'lolz.txt', someData),
writeFile2 : fs.writeFile.bind(fs, 'lol2z.txt', someData),
}, function (err){
console.log('finished')
});
These two implementations are identical.
Performance
Just check these out:
http://jsperf.com/bind-vs-call2
http://jsperf.com/js-bind-vs-closure/2
http://jsperf.com/call-vs-closure-to-pass-scope/10
bind has a big performance overhead comparing to other types of calling, but make sure you don't sacrifice performance with maintainability with pre-mature optimizations.
Also you can have a look at this article.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Can I get the name of the currently running function in javascript?
I need this for recursion. I'd like to be able to change the function name without checking and changing every instance where the function calls itself.
(For example php has "magic constants" like __FUNCTION__ etc.. - is something similar in JavaScript?)
If your goal is recursion, you don't need the function name as a string if you can get a reference to the function itself. Note that you'll still have to check and change every instance where the function is called by others, and that's likely to be a larger task than updating the recursive calls (if for no other reason than it's not localized to the function body).
Passing the function as an argument
function foo(self, i)
{
if (i === 0 )
return;
console.log(i--);
self(self, i);
}
foo(foo, 3);
Using arguments.callee (As Raynos points out, this is brittle in strict mode)
function foo(i)
{
if (i === 0 )
return;
console.log(i--);
arguments.callee(i);
}
foo(3);
Output of either option
3
2
1
Maybe you can refactor your function since arguments.callee is not dependable. For example, you could use a nested function that does the recursion:
var name_does_not_matter = function(m) {
var inner = function(n) {
if (n <= 2) return 1;
return inner(n-2) + inner(n-1);
};
return inner(m);
};
[UPDATE] Actually, you should be able to access the function by its name regardless of the parent scope. In my test, the following example works:
var foo = 10;
var bar = function foo(n) {
return (n <= 2) ? 1 : foo(n-2) + foo(n-1);
};
alert(foo); // Displays '10'
alert(bar(10)); // Displays '55'
function senad()
{
var fName= arguments.callee.toString();
fName= fName.substr('function '.length);
fName= fName.substr(0, fName.indexOf('('));
alert(fName)
}
senad();
(function() {
"use strict";
console.log(arguments.callee);
})()
Yields
TypeError: Cannot access property 'callee' of strict mode arguments
You cannot do this in ES5 strict mode, and for a good reason. It's a hack. Don't do it.
EDIT: OK, I believe the following solutions are valid:
Use the jQuery AOP plugin. It basically wraps the old function together with the hook into a function sandwich and reassigns it to the old function name. This causes nesting of functions with each new added hook.
If jQuery is not usable for you, just pillage the source code, there did not seem to be any jQuery dependencies in the plugin, and the source is simple and very small.
Have an object describing all hooks and their targets and one to store the initial unmodified function. When adding a new hook, the wrapping would be redone around the original function, instead of re-wrap the the previous wrapping function.
You escape nested functions, and get two objects to handle instead. Potentially, this could also mean easier hook handling, if you add/remove hooks often and out of order.
I'll go with the first, since it's already done, and I don't have performance to worry about. And since the original functions are not affected, even if I switch hooking methods, I'll only need to redo the hook adding, which might be just some simple search&replace operations.
Hi,
Is it possible to create a mechanism, in which function A might have a set of hooks(functions that will execute before/after function A)?
Ideally, function A would not be aware of hooking functionality, so that I do not have to modify the source code of function A to call the hooks. Something like:
A = function(){
alert("I'm a naive function");
};
B = function(){
alert("I'm having a piggyback ride on function A!"+
"And the fool doesn't even know it!");
};
addHook(B, A)//add hook B to function A
A()
//getting alerts "I'm a naive function"/"I'm having a
//piggyback ride on function A! And the fool doesn't even know it!"
I've been trying to hack something up for a couple of hours, but so far no luck.
Might not be pretty but it seems to work...
<script>
function A(x) { alert(x); return x; }
function B() { alert(123); }
function addHook(functionB, functionA, parent)
{
if (typeof parent == 'undefined')
parent = window;
for (var i in parent)
{
if (parent[i] === functionA)
{
parent[i] = function()
{
functionB();
return functionA.apply(this, arguments)
}
break;
}
}
}
addHook(B, A);
A(2);
</script>
Take a look at jQuery's AOP plugin. In general, google "javascript aspect oriented programming".
Very simple answer:
function someFunction() { alert("Bar!") }
var placeholder=someFunction;
someFunction=function() {
alert("Foo?");
placeholder();
}
This answer is not definitive, but rather demonstrative of a different technique than those offered thus far. This leverages the fact that a function in Javascript is a first-class object, and as such, a) you can pass it as a value to another function and b) you can add properties to it. Combine these traits with function's built-in "call" (or "apply") methods, and you have yourself a start toward a solution.
var function_itself = function() {
alert('in function itself');
}
function_itself.PRE_PROCESS = function() {
alert('in pre_process');
}
function_itself.POST_PROCESS = function() {
alert('in post_process');
}
var function_processor = function(func) {
if (func.PRE_PROCESS) {
func.PRE_PROCESS.call();
}
func.call();
if (func.POST_PROCESS) {
func.POST_PROCESS.call();
}
}
The following function will give you before and after hooks that can be stacked. So if you have a number of potential functions that need to run before the given function or after the given function then this would be a working solution. This solution does not require jQuery and uses native array methods (no shims required). It should also be context sensitive so if you are calling the original function with a context if should run each before and after function likewise.
// usage:
/*
function test(x) {
alert(x);
}
var htest = hookable(test);
htest.addHook("before", function (x) {
alert("Before " + x);
})
htest.addHook("after", function (x) {
alert("After " + x);
})
htest("test") // => Before test ... test ... After test
*/
function hookable(fn) {
var ifn = fn,
hooks = {
before : [],
after : []
};
function hookableFunction() {
var args = [].slice.call(arguments, 0),
i = 0,
fn;
for (i = 0; !!hooks.before[i]; i += 1) {
fn = hooks.before[i];
fn.apply(this, args);
}
ifn.apply(this, arguments);
for (i = 0; !!hooks.after[i]; i++) {
fn = hooks.after[i];
fn.apply(this, args);
}
}
hookableFunction.addHook = function (type, fn) {
if (hooks[type] instanceof Array) {
hooks[type].push(fn);
} else {
throw (function () {
var e = new Error("Invalid hook type");
e.expected = Object.keys(hooks);
e.got = type;
return e;
}());
}
};
return hookableFunction;
}
Here's what I did, might be useful in other applications like this:
//Setup a hooking object
a={
hook:function(name,f){
aion.hooks[name]=f;
}
}a.hooks={
//default hooks (also sets the object)
};
//Add a hook
a.hook('test',function(){
alert('test');
});
//Apply each Hook (can be done with for)
$.each(a.hooks,function(index,f){
f();
});
I don't know if this will be useful. You do need to modify the original function but only once and you don't need to keep editing it for firing hooks
https://github.com/rcorp/hooker
I have a function, a(), that I want to override, but also have the original a() be performed in an order depending on the context. For example, sometimes when I'm generating a page I'll want to override like this:
function a() {
new_code();
original_a();
}
and sometimes like this:
function a() {
original_a();
other_new_code();
}
How do I get that original_a() from within the over-riding a()? Is it even possible?
Please don't suggest alternatives to over-riding in this way, I know of many. I'm asking about this way specifically.
You could do something like this:
var a = (function() {
var original_a = a;
if (condition) {
return function() {
new_code();
original_a();
}
} else {
return function() {
original_a();
other_new_code();
}
}
})();
Declaring original_a inside an anonymous function keeps it from cluttering the global namespace, but it's available in the inner functions.
Like Nerdmaster mentioned in the comments, be sure to include the () at the end. You want to call the outer function and store the result (one of the two inner functions) in a, not store the outer function itself in a.
The Proxy pattern might help you:
(function() {
// log all calls to setArray
var proxied = jQuery.fn.setArray;
jQuery.fn.setArray = function() {
console.log( this, arguments );
return proxied.apply( this, arguments );
};
})();
The above wraps its code in a function to hide the "proxied"-variable. It saves jQuery's setArray-method in a closure and overwrites it. The proxy then logs all calls to the method and delegates the call to the original. Using apply(this, arguments) guarantees that the caller won't be able to notice the difference between the original and the proxied method.
Thanks guys the proxy pattern really helped.....Actually I wanted to call a global function foo..
In certain pages i need do to some checks. So I did the following.
//Saving the original func
var org_foo = window.foo;
//Assigning proxy fucnc
window.foo = function(args){
//Performing checks
if(checkCondition(args)){
//Calling original funcs
org_foo(args);
}
};
Thnx this really helped me out
You can override a function using a construct like:
function override(f, g) {
return function() {
return g(f);
};
}
For example:
a = override(a, function(original_a) {
if (condition) { new_code(); original_a(); }
else { original_a(); other_new_code(); }
});
Edit: Fixed a typo.
Passing arbitrary arguments:
a = override(a, function(original_a) {
if (condition) { new_code(); original_a.apply(this, arguments) ; }
else { original_a.apply(this, arguments); other_new_code(); }
});
The answer that #Matthew Crumley provides is making use of the immediately invoked function expressions, to close the older 'a' function into the execution context of the returned function. I think this was the best answer, but personally, I would prefer passing the function 'a' as an argument to IIFE. I think it is more understandable.
var a = (function(original_a) {
if (condition) {
return function() {
new_code();
original_a();
}
} else {
return function() {
original_a();
other_new_code();
}
}
})(a);
The examples above don't correctly apply this or pass arguments correctly to the function override. Underscore _.wrap() wraps existing functions, applies this and passes arguments correctly. See: http://underscorejs.org/#wrap
In my opinion the top answers are not readable/maintainable, and the other answers do not properly bind context. Here's a readable solution using ES6 syntax to solve both these problems.
const orginial = someObject.foo;
someObject.foo = function() {
if (condition) orginial.bind(this)(...arguments);
};
I had some code written by someone else and wanted to add a line to a function which i could not find in the code. So as a workaround I wanted to override it.
None of the solutions worked for me though.
Here is what worked in my case:
if (typeof originalFunction === "undefined") {
originalFunction = targetFunction;
targetFunction = function(x, y) {
//Your code
originalFunction(a, b);
//Your Code
};
}
I've created a small helper for a similar scenario because I often needed to override functions from several libraries. This helper accepts a "namespace" (the function container), the function name, and the overriding function. It will replace the original function in the referred namespace with the new one.
The new function accepts the original function as the first argument, and the original functions arguments as the rest. It will preserve the context everytime. It supports void and non-void functions as well.
function overrideFunction(namespace, baseFuncName, func) {
var originalFn = namespace[baseFuncName];
namespace[baseFuncName] = function () {
return func.apply(this, [originalFn.bind(this)].concat(Array.prototype.slice.call(arguments, 0)));
};
}
Usage for example with Bootstrap:
overrideFunction($.fn.popover.Constructor.prototype, 'leave', function(baseFn, obj) {
// ... do stuff before base call
baseFn(obj);
// ... do stuff after base call
});
I didn't create any performance tests though. It can possibly add some unwanted overhead which can or cannot be a big deal, depending on scenarios.
So my answer ended up being a solution that allows me to use the _this variable pointing to the original object.
I create a new instance of a "Square" however I hated the way the "Square" generated it's size. I thought it should follow my specific needs. However in order to do so I needed the square to have an updated "GetSize" function with the internals of that function calling other functions already existing in the square such as this.height, this.GetVolume(). But in order to do so I needed to do this without any crazy hacks. So here is my solution.
Some other Object initializer or helper function.
this.viewer = new Autodesk.Viewing.Private.GuiViewer3D(
this.viewerContainer)
var viewer = this.viewer;
viewer.updateToolbarButtons = this.updateToolbarButtons(viewer);
Function in the other object.
updateToolbarButtons = function(viewer) {
var _viewer = viewer;
return function(width, height){
blah blah black sheep I can refer to this.anything();
}
};
Not sure if it'll work in all circumstances, but in our case, we were trying to override the describe function in Jest so that we can parse the name and skip the whole describe block if it met some criteria.
Here's what worked for us:
function describe( name, callback ) {
if ( name.includes( "skip" ) )
return this.describe.skip( name, callback );
else
return this.describe( name, callback );
}
Two things that are critical here:
We don't use an arrow function () =>.
Arrow functions change the reference to this and we need that to be the file's this.
The use of this.describe and this.describe.skip instead of just describe and describe.skip.
Again, not sure it's of value to anybody but we originally tried to get away with Matthew Crumley's excellent answer but needed to make our method a function and accept params in order to parse them in the conditional.