CODEWITHSUNDEEP
javascript
user2211703
user2211703

Reputation: 487

javascript: own function is not defined in map

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?

Upvotes: 2

Views: 580

Answers (3)

smnbbrv
smnbbrv

Reputation: 24531

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));

Upvotes: 1

bitifet
bitifet

Reputation: 3659

double is a property of Number prototype, not a global variable.

x.map(function(y){return y.double()});

Upvotes: 0

RichieHindle
RichieHindle

Reputation: 281385

You need to call your method on an instance of Number:

...
console.log(x.map(function (n) { return n.double(); }));

Upvotes: 0

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