CODEWITHSUNDEEP
javascript
Misha Reyzlin
Misha Reyzlin

Reputation: 13916

Array literal methods invocation and object literal methods invocation difference

In JavaScript, I wonder why I can do this:

[].slice.apply([1,2,3], [0, 2]) // returns [1, 2]

Which is as far as I understand equivalent of this:

Array.prototype.slice.apply([1,2,3], [0, 2]); // returns [1, 2]

But I can't do this:

{}.hasOwnProperty.apply(a, ['a']);

Which would allow to not type this long line:

Object.prototype.hasOwnProperty.apply(a, ['a']); // returns true or false

Well, while I am at it, I also see that I can actually do all of these:

''.indexOf.apply('asdasd', ['s']); // returns 1
true.toString.apply(true); // returns // "true" as string

What the deal with {} ? :-) Why is it special?

Upvotes: 0

Views: 256

Answers (3)

Matt Ball
Matt Ball

Reputation: 360026

Is hasOwnProperty('a') a typo?

{}.hasOwnProperty.apply(a, ['a']);

But that doesn't quite work due to JavaScript interpreting {} as block delimiters. Just add parentheses:

({}).hasOwnProperty.apply(a, ['a']);

Check it:

> var a = {'a': 1}
  Object
> {}.hasOwnProperty.apply(a, ['a']);
  SyntaxError: Unexpected token .
> ({}).hasOwnProperty.apply(a, ['a']);
  true

Upvotes: 6

davin
davin

Reputation: 45565

Brackets:

({}).hasOwnProperty.apply({k:9,aa:5}, ['a']); // false
({}).hasOwnProperty.apply({k:9,a:5}, ['a']); // true

Upvotes: 2

Jordan
Jordan

Reputation: 32552

hasOwnProperty() returns true or false, not the actual property itself.

With your other examples, you are working with functions that are returned, not scalars or native objects, which is why you can call apply() on them.

Have you tried {}.hasOwnProperty.apply(......)?

Upvotes: 2

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