Does Javascript allocate 32 bits of memory for variables with an undefined value?

Question

Suppose I have the following function signature:

function test(varible1, varible2) {}

When I call it I pass only one parameter:

test(5);

So within test function the variable2 still be created but will have value of undefined. I'm wondering if js engine still allocates 32 bit in the memory for that variable?

JS arrays are sparse, and the argument array of a function call is some sort of array. So probably not. — Renan Le Caro
– Renan Le Caro, Commented Feb 16, 2015 at 16:55
To know definitively you'll need someone who's familiar with the internals of an ECMAScript implementation because the spec it's self isn't super clear on the subject (or you'll need to test it your self). What I can say is that any variable, pre-defined or not, with no value will be undefined - so my guess is no, they don't. — Dan Smith
– Dan Smith, Commented Feb 16, 2015 at 16:57
Which JS engine? There are lots. This is an implementation detail, not something determined by the specification. — Quentin
– Quentin, Commented Feb 16, 2015 at 17:03
@Quentin, V8 for example. Can you say anything about one that you know? — Max Koretskyi
– Max Koretskyi, Commented Feb 16, 2015 at 17:05

Luggage · Accepted Answer · 2015-02-16 17:30:55Z

1

I can't find the size of undefined and I'm sure it varies with engine, but I assume that the best case is 32 bits. The variable exists, so it needs a value to even know it's undefined. That value is very likely a pointer which will be 32 or 64 bits.

answered Feb 16, 2015 at 17:30

Luggage

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1 Comment

Ludwik Over a year ago

My first guess was 32 on 32 systems, 64 on 64 systems. But AFAIK there's no reason it would not allocate space, even if the value is undefined.

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