http://wiki.ecmascript.org/doku.php?id=harmony:rest_parameters
Hi,
Here is the behavior I would like:
function f( a, b, ...rest ) { }
f( 1, 1 );// ok
f( 1, 1, 1 );// ok
f( 1, undefined );// ok
f( 1 );// Error: missing parameter
Because since you can't reference a and b as properties of an object
anymore, there is no way you can know whether they are undefined
because the value given was undefined or because no value was given.
Of course, no such error would happen if there is a default value:
function f( a, b=1, ...rest ) { }
---------------------------------------------------
If you consider throwing an error a bit too harsh, you should consider
giving arguments.length. Not withing arguments but as a separate
variable.
function f( a, b, ...rest ) {
var awesomeNameYoullFind = f.length + rest.length; // this should
be provided by core
if ( awesomeNameYoullFind < 2 ) {// and people who want to throw
errors will have a convenient way of doing it
throw Error();
}
}
-----------------------------------------------------
Another thing I think arguments shouldn't disappear. It sucks that it
isn't an array but it still has some use-cases.
e.g. a function that delegates in certain conditions
function f( a, b, ...rest ) {
if ( a ) {
f2.apply( this, arguments );
// or f2( ...arguments );
} else {
// w/e
}
}
This could be done that way:
function f( a, b, ...rest ) {
if ( a ) {
f2( a, b, ...rest );
} else {
// w/e
}
}
But what if you have a, b, c, d and so on? You don't want to copy all
those variable names.
And what if you want to delegate everything except a and b? Without an
argu,ments object, it's bothersome. With it, you just slice from index
2...
To give a real example: assertions.
I use to do things like that:
function f( a, b, c, d ) {
assertArguments( arguments, [
{// a
type: 'number'
},
{// b and c
type: 'string',
length: 2
},
{// d
type: 'object',
optionnal: true
}
] );
}
And if you remove the arguments object, it gets really bothersome...
You have to make sure you pass every single arguments in the good
order...
------------------------------------------------------------
But of course, it should become a real array (and probably change its
name to args or something similar). And to prevent from breaking
existing codes, if there is already a variable named args in the scope
or a parent scope *and it is not the args created for another
function*, replace it.
var args = 1;
function f( ) {
// here args is 1 no matter what
}
f(0);
function f1( ) {
// here args is the arguments from f1
function f2( ) {
// here args is the arguments from *f2*
// because even though it was in the scope, some magic
happened and the engine figured out it wasn't a variable declared by
the user
}
f2(2);
}
f1(1);
--------------------------------------------------------
PS: If a new arguments object is created, then there is no use for
awesomeNameYoullFind.
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