javascript: do primitive strings have methods?

Question

MDN states:

primitive, primitive value

A data that is not an object and does not have any methods. JavaScript has 5 primitive datatypes: string, number, boolean, null, undefined. With the exception of null and undefined, all primitives values have object equivalents which wrap around the primitive values, e.g. a String object wraps around a string primitive. All primitives are immutable.

So when we call a "s".replace or "s".anything is it equivalent to new String("s").replace and new String("s").anything?

Pointy · Accepted Answer · 2011-04-22 02:31:04Z

17

No, string primitives do not have methods. As with numeric primitives, the JavaScript runtime will promote them to full-blown "String" objects when called upon to do so by constructs like:

var space = "hello there".indexOf(" ");

In some languages (well, Java in particular, but I think the term is in common use) it's said that the language "boxes" the primitives in their object wrappers when appropriate. With numbers it's a little more complicated due to the vagaries of the token grammar; you can't just say

var foo = 27.toLocaleString();

because the "." won't be interpreted the way you'd need it to be; however:

var foo = (27).toLocaleString();

works fine. With string primitives — and booleans, for that matter — the grammar isn't ambiguous, so for example:

var foo = true.toString();

will work.

edited Apr 22, 2011 at 2:31

answered Apr 22, 2011 at 2:25

Pointy

415k62 gold badges600 silver badges631 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Pacerier Over a year ago

heys btw is the double dot syntax "standard" ? Like 27..toLocaleString()

Pointy Over a year ago

Well it seems to work in Chrome at least ... the issue is that the low-level "token grammar" will hook the first "." onto the number, because of the way floating-point numbers look ("23.223"). But that double-dot trick should work, because the tokenizer will stop at the second ".", leaving it to the parser to construct the property reference expression.

Pointy Over a year ago

Personally, I'd prefer (27).toLocaleString() because it's easy to lose track of a little "." stuck in there. But that's just a stylistic opinion and it isn't worth much :-)

kennebec Over a year ago

The first dot after a digit is a decimal point. All browsers have always agreed that 12..toLocaleString() is operating on the number.

Pointy Over a year ago

@kennebec that makes good sense, thanks; I haven't personally been keeping track over the past dozen years, but it certainly makes sense given the token grammar etc. :-)

|

helloandre · Accepted Answer · 2011-04-22 02:29:23Z

8

The technically correct answer is "no".

The real-world answer is "no, but it will work anyway". That's because when you do something like

"s".replace()

the interpreter knows that you want to actually operate on the string as if you had created it with

var str = new String("s")

and therefore acts as if you had done that.

answered Apr 22, 2011 at 2:29

helloandre

10.8k9 gold badges50 silver badges64 bronze badges

Collectives™ on Stack Overflow

javascript: do primitive strings have methods?

2 Answers 2

7 Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

Comments

Linked

Related