The required validator is the only validator that ensures a value is present. All other validators in Strickland will return isValid: true if the value supplied is empty. This approach allows all other validators to be applied to optional values. And as we'll explore shortly, validators can be composed to combine required with other validators.

The values that required recognizes as empty and invalid are:

1. null

2. undefined

3. '' (empty string)

4. false

For all other values, including 0 (despite being is falsy), required will indicate the result is valid.

The false boolean value being invalid is commonly used to validate that checkboxes must be checked. For example, when a user must accept terms before submitting a form, the checked state of the checkbox can be validated with required.

Named Props

• required: A boolean indicating whether or not the value is required (default: true)

Parameters

The required validator supports three parameter signatures:

1. required(requiredValue) where the value is used as the required named prop

2. required(propsObject) where the props object contains a required named prop

3. required(propsFunction) where the props function returns a props object with a required named prop

Usage

import validate, {required} from 'strickland';
​
const nameRequired = required({
    message: 'Name is required'
});
​
const result = validate(nameRequired, '');
​
/*
    result = {
        required: true,
        message: 'Name is required',
        isValid: false,
        value: ''
    }
 */

The required validator respects a named prop of required that indicates whether or not the value is required. This is useful for dynamic validation scenarios where your application needs to support conditionally required fields; you can apply the required validator and dynamically supply the required named prop. If the required named prop is false, the validator will always return isValid: true.

// Required by default
const a = required();
​
// As a value parameter
const requiredField = required(true);
const optionalField = required(false);
​
// As a named prop
const nameRequired = required({
    required: true,
    message: '"Name" is required'
});
​
// As a function that resolves to have the named prop
const requiredValidator = required((context) => ({
    required: context.required,
    message: context.required ?
        '"Name" is required' :
        '"Name" is optional'
}));