Undocumented message function has a bug

[ianchanning]

I wanted to be able to use values in the error message - and although not documented in the README it is supported.

However there is a bug because in createFormValidation.js#L43:

            let finalMessage = defaultMessage
            if (typeof message === 'function') {
                finalMessage = message(value, values, options)
            }
            if (typeof message !== 'undefined') {
                finalMessage = message
            }

... you're mutating finalMessage and message is a function, first finalMessage is set to the return value of message and then it is set again to be the function itself.

[ianchanning]

There is actually a workaround to this bug which another undocumented feature where you can specify your entire own createFieldValidation function.

You could maybe document this too 🙂

/**
 * Generate the field validation function
 *
 * @param {function} validate boolean function that checks the form value
 * @param {function|string} message Either function that gives an error message based on the value or else error message
 * @param {string} defaultMessage if message is undefined
 * @returns {function} (string, array, object) => [{ path, message }] The field validation function itself
 */
const createFieldValidation =
    (validate, errorMessage, defaultMessage = 'Invalid') =>
    (path, values, options) => {
        const value = values[path]
        const formatMessage = () => {
            if (typeof errorMessage === 'function') {
                return errorMessage(value, values, options)
            }
            return typeof errorMessage === 'undefined'
                ? defaultMessage
                : errorMessage
        }
        if (typeof value === 'undefined' || validate(value, values, options)) {
            return []
        }
        return [{ path, message: formatMessage() }]
    }

You can then specify this as the validation function in the formRule object, instead of validate and message.

const validation = createFormValidation([
    {
        path: 'code',
        validate: isRequired,
        message: <Trans>Please enter a code</Trans>,
    },
    {
        path: 'code',
        validation: createFieldValidation(
            preformat(getLength(invalidNumbers), isEqualTo(0)),
            // message format
            (code) =>
                `${t`Invalid numbers`}: '${invalidNumbers(code)
                    .split('')
                    .join(',')}'`
        ),
    },
])