This question already has an answer here:
Using function.prototype.bind directly on function declaration
(1 answer)
Closed 7 years ago.
I have been programming in JS for about a year, and I swear there was a way to do this:
function a(){
}.bind(this);
or
function a(){
}.apply(this,null);
I can do this:
(function a(){
console.log('b');
}).apply(null);
a(); //but this will throw an error
is there a way to do what I am trying to do? I just want to invoke apply, call or bind on a function without losing scope.
Are you looking for
var a = function a() {
// ...
}.bind(this);
? You can't use a function as an expression in the context of a function declaration statement; the syntax just doesn't allow it. However, you can get an effect very similar to a function declaration statement by instantiating the function in an expression and assigning the reference to a local variable, as above. When you do that, your function is instantiated in the context of an expression, and so using it as an object base to call .bind() works fine.
Related
This question already has answers here:
Why use named function expressions?
(5 answers)
What's the point of naming function expressions if you can't really reference them by the names you give them? [duplicate]
(5 answers)
Closed 5 years ago.
var boo= function foo(){
console.log("I am foo");
}
boo(); // output: I am foo
foo(); // output: Uncaught ReferenceError
I am little confused with javascript named function. Can any one please explain why in above code snippet the foo() function call is throwing the error. Thanks in advance
var boo= function foo(){
There is a clear difference between a function and function expression.
What you have is an expression resolved to a variable. The way you are expecting to work needs to be a function or a variable resolved by a function expression.
From MDN docs
Here is an example of an anonymous function expression (the name is
not used):
var myFunction = function() {
statements
}
It is also possible to provide a name inside the definition in order
to create a named function expression:
var myFunction = function namedFunction(){
statements
}
One of the benefit of creating a named function expression is that in
case we encounted an error, the stack trace will contain the name of
the function, making it easier to find the origin of the error.
As we can see, both example do not start with the function keyword.
Statements involving functions which do not start with function are
function expressions.
This question already has answers here:
Explain the encapsulated anonymous function syntax
(10 answers)
Closed 6 years ago.
Lets assume we have
function () {}.bind(null);
and
(function () {}).bind(null);
Why the first one doesn't work in developer console (it throws syntax error) but both of them work in code (".js" file in website).
I think its because you are trying to define an anonymous function. Console has no future way of referencing it so its a pointless endeavour, youre defining a function you have no way of calling. If you define it as a variable it works:
var a = function () {}.bind(null);
Also I dont think its binding related. Defining an anonymous function without binding and you have the same error
Edits
A statement that begins with the keyword "function" must be a valid
function declaration statement. That requires a name for the function.
In an expression (or expression statement), that rule is different; no
name is necessary because the function acts as a value in that
context. No name is required then.
via #Pointy from this answer
A function declaration cannot be anonymous, but a function expression
can. A stand alone anonymous function looks like a function
declaration that is missing an identifier to JavaScript. But, combined
with an operator, JavaScript treats an anonymous function as the
operator's operand expression.
via #gilly3 from this answer
This question already has answers here:
var functionName = function() {} vs function functionName() {}
(41 answers)
What is the difference between a function expression vs declaration in JavaScript? [duplicate]
(5 answers)
Closed 8 years ago.
I couldnT find an answer easily, so even if this question is a dupe, the answers donT come up using these keywords.
I want to know the difference between the different way of declaring functions in a sample app.js
var foo = function()
{
//..
}
function bar()
{
//..
}
var baz= function()
{
//..
}
function qux()
{
//..
}
// other??
I m also not clear about the scope where I can use each function. Thanks!
There are four ways to create a function in JavaScript.
Function declaration
This will create a variable foo in the current scope and assign a named function to it.
function foo () {
}
Function declarations are hoisted so it doesn't matter where, in the applicable scope, you put them. It is considered good coding practise to define them before you use them though.
Anonymous function expression
This will create a function without a name and use it in an expression. In this example it is assigned to the variable something.
something = function () {
};
Named function expression
This is the same as an anonymous function expression except that it has a name, creates a variable of that name in the scope of itself and is horribly broken in older versions of Internet Explorer.
something = function foo () {
};
Function constructor
Do not use function constructors. They are eval by another name. You can read about them on MDN if you're interested.
This question already has answers here:
Why JavaScript function declaration (and expression)?
(5 answers)
Closed 8 years ago.
I'm assigning a named function expression to a property of an object:
var foo = {};
foo.bar = function bar(){
console.log('bar');
};
foo.bar() => bar
bar() => ReferenceError: bar is not defined
Why can't I call bar() directly, why isn't it defined?
I know that I can simply chain the assignment like var bar = foo.bar = function(){}, so I'm not looking for a work-around or other solution, I'm only interested in why it doesn't work.
I've tested in Chrome console and Node.JS.
Named function expressions are simply not supposed to work that way. The function name is only visible inside the function, not outside.
A function instantiation expression that happens to have a name is not the same thing as a function declaration statement. Those are two distinct syntactic (and semantic) entities in the language.
This question already has answers here:
var functionName = function() {} vs function functionName() {}
(41 answers)
Why use named function expressions?
(5 answers)
Closed 9 years ago.
I'm going through this blog about the difference between function declarations and function expressions.
It gives these two examples. They call the first an "anonymous function expression" and the second a "named function expression."
// anonymous function expression
var a = function(){
return 3;
}
// named function expression
var b = function bar(){
return 3;
}
I tested these two in Chrome's JS console and I see the following:
a()
=> 3
b()
=> 3
bar()
=> bar is not defined
My question is: In the second function expression declaration, what is the point of "bar"? In general, why does one ever use a named function expression?
Some people prefer to do it like this because if errors occur, your functions have names. It's mostly a matter of preference and how often you have trouble with unnamed functions.
You don't normally see it used in a var declaration, but instead when declaring callbacks:
callbackFunction(function success() { ... }, function fail() { ... })
That way you know which argument is which, they're labelled, and if one of them fails you get a precise indication of which one broke.
var b = function bar(){
return 3;
}
bar()
=> bar is not defined
The identifier bar is only available inside of the function. Try
var b = function bar() {
console.log(bar);
}
b();
why does one ever use a named function expression?
To allow referencing a function expression that was not assigned to a reachable or constant variable, e.g. for recursion in an IEFE.
Also, named functions show up different during debugging, e.g. in call stack (trace)s or breakpoint listings. Often you can use a (named) function declaration instead of a function expression, see also http://blog.niftysnippets.org/2010/03/anonymouses-anonymous.html.