How to provide different error messages for min, max in isLength type validation under checkSchema of express-validator

Question

I am looking for a solution to provide different error messages in express-validator where the options can contain more than one value like isLength which can take min and max value.

var validation_rules = checkSchema({
    first_name: {
        notEmpty: {
            errorMessage: 'The First Name field is required'
        },
        isString: {
            errorMessage: 'The First Name must be a string.'
        },
        isLength: {
            options: { min: 3, max: 4 }
        }
    }
});

As my example, I want to provide different error messages for min and max validation.

for min - The First Name must be at least 3 characters.

for max - The First Name may not be greater than 50 characters.

But I can only provide a single errorMessage here which is commonly used for both types of validation.

Can someone tell me how this can possible in express-validator checkSchema validation?

Answer 1

You can do it by creating a custom validator. In this custom validator check the length of your First-name with different conditions and for each invalid conditions reject with a promise your error message.

var validation_rules = checkSchema({
    first_name: {
        notEmpty: {
            errorMessage: 'The First Name field is required'
        },
        isString: {
            errorMessage: 'The First Name must be a string.'
        },
        custom: value => {
            if (value.length < 3) {
             return Promise.reject("The First Name is too short")
            } else if (value.length > 4) {
             return Promise.reject("The First Name is too long")
            }
            return Promise.resolve()
        }
    }
});