js: replace push.apply with for loop for string add [backport]
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Thanks for your hard work on this PR! Hint: mm: orc; opt: speed; options: -d:release |
narimiran
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Nov 8, 2025
) While `a.push.apply(a, b)` is better for performance than the previous `a = a.concat(b)` due to the fact that it doesn't create a new array, there is a pretty big problem with it: depending on the JS engine, if the second array is too long, it can [cause a crash](https://tanaikech.github.io/2020/04/20/limitation-of-array.prototype.push.apply-under-v8-for-google-apps-script/) due to the function `push` taking too many arguments. This has unfortunately been what the codegen produces since 1.4.0 (commit 707367e). So string addition is now moved to a compilerproc that just uses a `for` loop. From what I can tell this is the most compatible and the fastest. Only potential problem compared to `concat` etc is with aliasing, i.e. adding an array to itself, but I'm guessing it's enough that the length from before the iteration is used, since it can only grow. The test checks for aliased nim strings but I don't know if there's an extra protection for them. (cherry picked from commit 839cbeb)
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While
a.push.apply(a, b)is better for performance than the previousa = a.concat(b)due to the fact that it doesn't create a new array, there is a pretty big problem with it: depending on the JS engine, if the second array is too long, it can cause a crash due to the functionpushtaking too many arguments. This has unfortunately been what the codegen produces since 1.4.0 (commit 707367e).So string addition is now moved to a compilerproc that just uses a
forloop. From what I can tell this is the most compatible and the fastest. Only potential problem compared toconcatetc is with aliasing, i.e. adding an array to itself, but I'm guessing it's enough that the length from before the iteration is used, since it can only grow. The test checks for aliased nim strings but I don't know if there's an extra protection for them.