I get the following error ReferenceError: double is not defined
Code:
Number.prototype.double = function (){
return this*2;
}
x=[1,2]
console.log(x.map(double));
how can i fix it?
-
You should really not extend or modify native javascript prototypes (it can create all kinds of unexpected side effects)nils– nils2015-06-05 09:11:48 +00:00Commented Jun 5, 2015 at 9:11
Add a comment
|
3 Answers
You can't do that like that. The reason is that this inside of map is not a number. That's why you cannot do it with a prototype like you wish.
What you can do is the following: get the passed parameter from map
Number.double = function (e){
return e*2;
}
x=[1,2]
console.log(x.map(Number.double));
EDIT: if you really need the prototype solution, you can do the following:
Number.prototype.double = function (e){
if (e) return e*2;
else return this*2;
}
x=[1,2]
console.log(x.map(Number.prototype.double));
2 Comments
RichieHindle
But
double() is now no longer a method of Number - this has changed the code completely. You can no longer say n.double() to double a number.
smnbbrv
@RichieHindle I don't think it changed the code, but I've added the solution for your case too. I actually think if it was used only for this specific case then there was no need to put it inside of the prototype; the first method just adds a
static method instead of member one.You need to call your method on an instance of Number:
...
console.log(x.map(function (n) { return n.double(); }));
Comments
double is a property of Number prototype, not a global variable.
x.map(function(y){return y.double()});
