Add validate property

[simonepri]

Proposal to add a validate property:

validate: (Function || Async Function) Receive the user input and answers of a chain.

Should return true if the value is valid, and an error message (String) otherwise.
If false is returned, a default error message is provided.

To do this we need to add a way to render errors messages.

API Usage Example:

validate: (input, answers) => {
  if (input === 'invalid') return 'The answer is invalid.';
  return true;  // Proceed to the next prompt of the chain if any.
}

[terkelg]

It's super important for me to keep the package really tight - without too many features or dependencies. What would the use case be for this?

I normally just do multiple prompts() and do validation after each.

That being said I've thinking about doing a message and split prompt.

[simonepri]

The main difference of doing the validation after the prompt is that you can't show live errors to users.

An example from inquirer:

Also it allows user to not have complicate logic to handle response rejection.

[lukeed]

Personally, I'd call this a maybe. As you've both mentioned, this requires an entirely new error-like module that might go beyond the scope of @terkelg's intentions.

A quick (and still manageable) way around this is to process prompts one at a time & then "validate" them on the onSubmit hook. You could choose to exit the prompt with an error (stdout.write('Reason'); return true) or display the same prompts definition, with an updated initial or message key.

function isCustom(val) {
  // return true if I consider valid
}

let defs = [
  {
    type: 'text',
    name: 'foobar',
    isValid: isCustom
  }, { 
    // ... etc
  }
];

function onSubmit(obj, val) {
  obj.isValid(val) && defs.shift(); // if valid, remove item
}

async function run() {
  if (!defs.length) return 'done';
  return await prompts(defs[0], { onSubmit }).then(run);
}

await run();

Not sure if the above will work 😆 Quick psuedo'ing

[simonepri]

It just feel too complicated to handle this manually for each prompt.
Also because the error is supposed to disappear after a valid input is provided.

[terkelg]

I'll take a look at this for a version v0.2. Feel free to add a PR

[yoavmmn]

Wait, whats wrong with options.onSubmit? It's built right into the API.
I think the only drawback is that you can't force the user to enter the expected input.

[yoavmmn]

Here's a little demonstration of the capabilities of options.onSubmit.

const prompts = require('prompts');

function isInputHiOrHey(greeting = '') {
  return greeting === 'hi' || greeting === 'hey';
}

// a recursive function that checks user's input just for the prompt named greeting
function checkInput(prompt, answer) {
  if (prompt.name === 'greeting') {
    if (!isInputHiOrHey(answer)) {
      console.log('Please enter a valid greeting.');
      prompts(prompt, { onSubmit: checkInput })
    }
  }
}

prompts({
  type: 'text',
  name: 'greeting',
  message: 'What\'s your greeting?'
}, {
  onSubmit: checkInput
});

[lukeed]

@yoavmmn That's essentially what my example is doing 😆 I agree, I think it's sufficient.

In order to display an error message, you could attach an onError key to each prompt, then change mine to:

function onSubmit(obj, val) {
  obj.isValid(val) ? defs.shift() : obj.onError();
}

Or handle all of that inside the isCustom function:

function isCustom(val) {
  if (val > 100) return true;
  console.log('ERROR MESSAGE');
  //=> returns undefined --> falsey
}

[yoavmmn]

@lukeed I have no idea how I missed your comment. Maybe because it's midnight already over here 😅

[tunnckoCore]

Just realized that the whole thing is that we need prop like onSubmit option but per question object. Then we can do anything from validate to required and etc.

[marcghorayeb]

Validate property would be nice yep 👍

[terkelg]

After #43 all prompts have a onSubmit and onAbort. It's in master but not yet released or documented. I'm still open for implementing some nice visuals for this later.

Focus right now is to get v0.1.5 out the door.

[dsevillamartin]

Sorry for the bump.

Is this feature still being considered?
Or at least, some method to make a custom implementation of it easier?

I would like to replace inquirer with this great module 🙂

[tunnckoCore]

@datitisev it was while ago.. Can't you use onSubmit to implement it?

[dsevillamartin]

@olstenlarck I haven't coded anything with prompts yet, and as this issue is still open, I thought maybe the end result was similar to validation (after reading all the comments), but not exactly.
Maybe I misread them, apologies if I did.
I'll see if I can implement it when I have the time.

[tunnckoCore]

I didn't tried onSubmit still either, but.. In glance looks it seems it would work.

[terkelg]

onSubmit is different from what @datitisev is asking for. I still want and need the filter myself. The feature is still being considered.

[terkelg]

validate option is added in v1.0.0 branch for Number and Text prompt.

const response = await prompts({
    type: 'number',
    name: 'value',
    message: 'How old are you?',
    validate: value => value < 18 ? `Nightclub is 18+ only` : true
});

Please give it a test run if you like @datitisev @lukeed @marcghorayeb

[dsevillamartin]

@terkelg Works great! 🙂 Thanks!

Edit: Not sure if it is a result from this change, but when the onCancel function returns true, it still exists.

[terkelg]

@datitisev is that a single prompt or a prompt chain?

[dsevillamartin]

@terkelg A single prompt.

  let onCancel = prompt => {
    console.log('Never stop prompting!');
    return true;
  }

  const response = await prompts({
      type: 'text',
      name: 'email',
      message: 'What\'s yar email?',
  }, { onCancel });

  console.log(response);

[terkelg]

onCancel is not preventing you from canceling a single prompt, it controls whether the prompt chain should cancel or continue. If you have an array of prompts you'll see it either continue or break the chain based on the onCancel return value.

[terkelg]

Coming in #80