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Weird behaviors of javascript: Primitive Types and Reference Types

MutluDev on August 19, 2020

I recently learned a difference between Primitive types and Reference types. I thought it would be great to write a blog post about this topic. ...

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Alex Janke • Aug 19 '20

pentacular • Aug 19 '20

There is no pass by reference in this article.

Alex Janke • Aug 19 '20

Not pass by (no functions in this article) but it's basically the same principle for types and assigning objects to new variables- still just a reference

pentacular • Aug 19 '20 • Edited

Not in the least.

let a = { v: 1 };
const foo = (p) => { p = { v: 2 }; };
foo(a);
console.log(a);

What does this print?

Which of your images does it reflect?

Alex Janke • Aug 19 '20 • Edited

What does this print?

An error. That is syntactically wrong

pentacular • Aug 19 '20

Try now ;)

Shane McGowan • Aug 20 '20

Nice write up! I wouldn't call these behaviors weird though, this is by far the least weird behavior of JavaScript

MutluDev • Aug 20 '20

Thanks, you're right this is not that weird, i wanted to make this as a series, i don't know what i will post next but i definitely consider "why 0.1 + 0.2 = 0.30000000000000004" which is lot weirder than this

Keff • Aug 20 '20 • Edited

It is weird. I'd love to know more about this!

It's not that weird actually. It's just how computers handle floating numbers.

Squeezing infinitely many real numbers into a finite number of bits requires an approximate representation. Although there are infinitely many integers, in most programs the result of integer computations can be stored in 32 bits. In contrast, given any fixed number of bits, most calculations with real numbers will produce quantities that cannot be exactly represented using that many bits.

Excerpt from this post: docs.oracle.com/cd/E19957-01/806-3...

Really interesting read, I had not read much about this whole topic!

MutluDev • Aug 20 '20

Yeah, it feels weird when you see it first, after you've learned how numbers work in JavaScript, everything makes sense.

youtube.com/watch?v=MqHDDtVYJRI
This video really helped me to grasp how numbers work in JavaScript,.

Excerpt from this post: docs.oracle.com/cd/E19957-01/806-3...

This looks really interesting I will read this, thanks.

pentacular • Aug 20 '20

Could you point out where 'reference types' are mentioned in the ecmascript spec?

I can't find it anywhere in the language specification.

MutluDev • Aug 20 '20

es5.github.io/#x8.7 this might help

pentacular • Aug 20 '20

It would if it talked about object references.

The references mentioned there are property references.

For example, in delete a.b; a.b is a reference.

"The Reference type is used to explain the behaviour of such operators as delete, typeof, and the assignment operators."

Can you find anything about 'reference types' that's relevant to object values or anything mentioned in this article?

To be specific, anywhere that supports the claim that objects, functions, and arrays are reference type values.

Selahattin Ünlü • Aug 21 '20

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Halil Dündar • Aug 19 '20

Very helpful and informative article, thank you for posting that.

MutluDev • Aug 19 '20

Thank you for your polite comment.