Promise already under evaluation: recursive default argument reference or earlier problems?

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When you see the error message “promise already under evaluation: recursive default argument reference or earlier problems?”, it means that you have encountered a recursive reference issue in your JavaScript code.

In JavaScript, recursive references occur when a function’s default argument value makes a reference to the same function. This can lead to unexpected behavior or even an infinite loop if not handled correctly.

Here’s an example to illustrate this issue: 

    
function exampleFunction(a = exampleFunction()) {
  return a;
}

console.log(exampleFunction());

In this example, the function exampleFunction has a default argument value of exampleFunction(). This means that if no argument is provided when calling the function, it will recursively call itself to generate the default value.

However, this code will result in the mentioned error because the default argument exampleFunction() is evaluated before the function is fully defined. Therefore, the promise is already under evaluation when the function is called, leading to the error.

To resolve this issue, you need to avoid recursive references in default arguments. You can accomplish this by using a separate value or function to handle the default case instead of relying on a self-reference.

Here’s an updated example that avoids the recursive reference issue: 

    
function exampleFunction(a = defaultValue()) {
  return a;
}

function defaultValue() {
  return "default value";
}

console.log(exampleFunction());

In this updated code, the default argument defaultValue() is a separate function that returns the desired default value. By doing so, we avoid the recursive reference and the code will execute without any errors.

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