fix: #24 Next.js SDK bad URL defaulting

[Draco1js]

Fixing the issue in #24 , should be a bit less error prone now

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[thomasballinger]

Unfortunately this doesn't work, in JavaScript passing undefined uses the default value just like not passing the variable!

tomb@macbookpro convex % node
Welcome to Node.js v18.20.6.
Type ".help" for more information.
> function foo(a=1) { return a; }
undefined
> foo(3)
3
> foo()
1
> foo(undefined)
1

I had a version of this in that caused a problem with Convex Auth, we could merge that again if we can confirm the Convex Auth issue is fixed?

[Draco1js]

I apologize, I thought I tested it pretty well the other day, can you see if you can break this function any way?

function getConvexUrl(
  deploymentUrl?: string | undefined
) {
  if (arguments.length === 0) {
    deploymentUrl = "ENV FALLBACK";
  }
  else if (deploymentUrl === undefined) { // Should skip over this if it hits the first one
    return `deploymentUrl is undefined, are your environment variables set?`;
  }

  return deploymentUrl;
}

console.log(getConvexUrl(), getConvexUrl(undefined), getConvexUrl("hello"));

This is what the output should look like:

ENV FALLBACK
deploymentUrl is undefined, are your environment variables set?
hello

[thomasballinger]

Cool, and thanks to get-convex/convex-auth#156 looks like the problem I had last time has been addressed. I think we need to roll it out carefully though since until now it was possible to pass undefined to mean "use the default." Could you make this console.error for now add a note to to the options documentation at

convex-backend/npm-packages/convex/src/nextjs/index.ts

Lines 65 to 69 in ade99cf

	/**
	* The URL of the Convex deployment to use for the function call.
	* Defaults to `process.env.NEXT_PUBLIC_CONVEX_URL`.
	*/
	url?: string;

that you should not pass undefined here, that passing undefined will throw an error in the future? And we'll make it an error in a few versions, probably the next minor version bump that requires explicit upgrade instructions so we can call it out.

It would be nice to add a TypeScript error when passing undefined explicitly but we can't expect https://www.typescriptlang.org/tsconfig/#exactOptionalPropertyTypes to be on for everyone so let's not.