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Why is dynamically adding properties slow in JavaScript?

Nick on February 06, 2022

JS gives an ability to add properties to the object after it was created. It gives a lot of freedom but has a performance cost at the same time. ...
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Josiah Bryan

You might want to fix your English in the title... Not exactly proper grammar, But no judgment, especially if English is not your first language!

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Nick

Thanks for such important feedback πŸ™πŸ»
Yep, English is my second language!
Can you tell what exactly should I fix in the title?

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Josiah Bryan

Absolutely! It's really simple, just change "does" to "is" and remove the 2nd "is".. I know verbs in English are weird, impressed that you've learned this much anyway! Here's the full title if you want to just copy and paste: "Why is dynamically adding properties slow in JavaScript?"

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Nick

Thanks a lot!
I truly appreciate your help πŸ™πŸ»

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Josiah Bryan

No worries, I remember when I lived in Israel and was learning Russian, it was so nice when people let me know a better way to say something. It also gave me incredible respect for anybody who learns another language because I know how hard it is myself haha

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Nick

What a coincidence, my first language is Russian! πŸ˜„

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LokiDev

I seriously love how two completely random dudes from completely different parts of the world just can get along, while politicians from all areas are just going mad :D.

I don't know you guys, but I love you :D

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Nick

Yeah, it’s so cool 😊

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Ilya Gorenburg

Pssst. Use free Grammarly for typos πŸ˜‰

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Nick

Thanks for the advice πŸ™πŸ»
I use it, but it doesn't detect this particular error for some reason.

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Omer

That's interesting. Thank you for the article!
You got me thinking about Typescript, maybe it could somehow help by introducing a new concept, like "typemap" I mean we have sourcemap that in dev time you can see for every js line the ts line that is associated with it. So maybe a typemap could tell for every line we have object declared, what should be the full shape of it. It could hint the js engine and maybe make it faster? πŸ€”

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Nick

You're welcome!

It sounds like an intriguing idea! I'll try to figure out how source maps work. And after it, I'll return with the answer! For now, I'm not sure whether it's possible or not.

Thanks for adding value to the conversation πŸ™πŸ»

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Varshneya Rao

Thank you for sharing a great article!
One note: it's useful to link some mdn/other docs regarding some of the specific terms used in the article. For example, transition chains are explained in more detail
Here: mathiasbynens.be/notes/shapes-ics
And here: v8.dev/blog/react-cliff

This article was the reason for me to dig into a lot of this reading material I would have otherwise not found by myself. Thank you again!

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Nick

You're welcome! πŸ™πŸ»

Thanks for the great suggestion! I'll do it from now on.

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Josiah Bryan

Also, really good article, I did not know about the performance impact of adding properties like that! Good tip! Thanks for being open to feedback on the English title haha

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Nick

Glad you like it!
You’re welcome! I’m still learning English, so I’m happy to get feedback on the grammar! πŸ™πŸ»

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Viraj Singh

Great article, well researched and the preact example is awesome πŸ‘

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Nick

Thank you πŸ™πŸ»
I really appreciate your compliment!

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Matthew Royal

Is it slower? How much slower? Linearly slower for each property added?

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Nick

A fair question. I'll try to provide stats/measurements in one of the future articles.
For now, I don't know the answers, because the topic is quite complex.

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jbaez

Interesting article, and very well explained. Thanks for sharing.

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Nick

Thank you πŸ™πŸ»
It’s my pleasure!

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Benny Schuetz

Nice one. Never thought of this before. Thanks for sharing!

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Nick

Thanks πŸ™πŸ»
I’m happy, you learned something new!