How much is the limit of Promise.all?

Question

Recently i got the following error while resolving a VERY large number of promises:

RangeError: Too many elements passed to Promise.all

I couldn't find any information regarding limits on MDN or ECMA-262.

Answer 1

According to the V8/V8 error code TooManyElementsInPromiseAll of the source code objects Promise

  T(TooManyElementsInPromiseAll, "Too many elements passed to Promise.all")

there is this limit. For the Promise.all i.e. the C++ PromiseAll we have there is a concept of MaximumFunctionContextSlots and kPromiseAllResolveElementCapabilitySlot, here it is the most interesting stuff from the source code:

// TODO(bmeurer): Move this to a proper context map in contexts.h?
  // Similar to the AwaitContext that we introduced for await closures.
  enum PromiseAllResolveElementContextSlots {
    // Remaining elements count
    kPromiseAllResolveElementRemainingSlot = Context::MIN_CONTEXT_SLOTS,

    // Promise capability from Promise.all
    kPromiseAllResolveElementCapabilitySlot,

    // Values array from Promise.all
    kPromiseAllResolveElementValuesArraySlot,

    kPromiseAllResolveElementLength
  };

I would expect to see a error throw like here

ThrowTypeError(context, MessageTemplate::TooManyElementsInPromiseAll);

Here it is the code that raise the TooManyElementsInPromiseAll error. Thank to Clarence that pointed me in the right direction!

BIND(&too_many_elements);
  {
    // If there are too many elements (currently more than 2**21-1), raise a
    // RangeError here (which is caught directly and turned into a rejection)
    // of the resulting promise. We could gracefully handle this case as well
    // and support more than this number of elements by going to a separate
    // function and pass the larger indices via a separate context, but it
    // doesn't seem likely that we need this, and it's unclear how the rest
    // of the system deals with 2**21 live Promises anyways.
    Node* const result =
        CallRuntime(Runtime::kThrowRangeError, native_context,
                    SmiConstant(MessageTemplate::kTooManyElementsInPromiseAll));
    GotoIfException(result, &close_iterator, var_exception);
    Unreachable();
  }

The check of this limit it is here

// Check if we reached the limit.
    TNode<Smi> const index = var_index.value();
    GotoIf(SmiEqual(index, SmiConstant(PropertyArray::HashField::kMax)),
           &too_many_elements);

so the kMax should solve the clue!