Why Is setTimeout Not Precise in JavaScript?

Why setTimeout Lacks Accuracy in JavaScript

JavaScript's setTimeout function is intended to execute code after a specified delay. However, the actual delay experienced can vary, especially between different computers.

Factors Limiting Accuracy

According to Mozilla Developer Network (MDN), setTimeout may not execute immediately after the expected delay due to factors such as:

• Browser Busyness: The browser's event loop may be occupied with other tasks, delaying the execution of setTimeout callbacks.

Browser Implementation Differences

Different browsers implement setTimeout differently. Tests show that Chrome and Firefox handle setTimeout execution slightly differently:

<code class="python">setTimeout(function() { console.log(Date.now() - date); }, 1000);

Browser   | Test1  | Test2  | Test3  | Test4
-------- | ------ | ------ | ------ | ------
Chrome    | 998    | 1014   | 998    | 998
Firefox   | 1000   | 1001   | 1047   | 1000</code>

Limitations of Date Type

The Date object used to measure the time difference between the expected and actual execution times may itself have some inaccuracy.

Conclusion

While setTimeout provides a convenient way to schedule delayed execution, it is not intended for precise timing due to the factors mentioned above. Developers should consider alternative solutions such as using requestAnimationFrame or external libraries like Tock for more accurate timing requirements.

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