Is increment an atomic operation in JavaScript?

Question

Is increment an atomic operation in JavaScript? If one thread is accessing ++i; and at the same time another one starts to access the operation will there be any problems?

JavaScript does not have threads. It does have workers (if you are in the right environment) (https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers) that can pass communications trough a message bus. — Jon Koops, Mar 30 '17 at 11:06

score 22 · Accepted Answer · answered Mar 30 '17 at 11:14

in Javascript always a function runs to completions that means if a function is running than it will run completely , only after that the other function will be called so , there is no chance of interleaving between statements( but in case of java it is different ) ,if you are confused with asynchronous execution than always remember async means later not parallel , So, coming to your problem, the answer is ,No you will not face any problem, it will be total atomic operation.

Do you have a source for this? – csvan Oct 29 '21 at 11:41 — csvan, Oct 29 '21 at 11:41

score 3 · Answer 2 · edited May 23 '17 at 12:17

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Javascript is single threaded, So you need to worry about deallocks or dirty read problems. Why doesn't JavaScript support multithreading?

edited May 23 '17 at 12:17

Community

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answered Mar 30 '17 at 11:12

Munish

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What about generator functions ? Surely you can exit a generator function before it have ended! – Hivaga Jun 21 '19 at 16:16

score 1 · Answer 3 · answered Mar 30 '17 at 11:08

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Javascript does not support multithreading. It may have web workers, but your question would not apply to this case, as workers do not share variables.

answered Mar 30 '17 at 11:08

Pierre-Rudolf Gerlach

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score -2 · Answer 4 · answered May 22 '20 at 13:53

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Yes there will be a problem. Even if Javascript is single threaded, i++ is (writer + modify + write) 3 steps operation, So when anyone is taking the i variable, the other one can set the modified i to the variable area. In order to solve this issue, you can use atomic variables instead of regular variable.

answered May 22 '20 at 13:53

Erdal76t

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JavaScript is single threaded, so how can any code "take" the variable `i` at the same time than other code is modifying it ? You need threads to access the same variable at the same time. – ingham Feb 08 '22 at 13:22
I'm not talking about the client side. In node.js, can you modify the global properties safely without using atomic variables? – Erdal76t Feb 09 '22 at 14:17

Is increment an atomic operation in JavaScript?

4 Answers4