A simple utility to validate objects (based off the Angular validation api)

validate.js

function validate(object, rules) {
    return Object.entries(object).reduce((errors, [key, value]) => {
        let validators = rules[key];
        
        if (!validators || validators.length === 0)
            return errors;

        if (typeof validators === 'function')
            validators = [validators];

        validators
            .map(validator => validator(value, object, key)) // run validators against the current value
            .filter(result => result.error) // select validation errors
            .forEach(result => errors[key] = { // merge validation errors into the accumulator
                ...errors[key],
                [result.error]: result.message
            });
        return errors;
    }, {});
}

function required(value) {
    const isValid = value !== undefined && value !== null && value !== '';
    return isValid || {error: 'required', message: `Please enter a value`};
}

function range(min, max, exclusive) {
    return function(value) {
        const skip = value === undefined || value === null || value === '';
        const isValid = skip || (
            exclusive 
                ? (value > min && value < max)
                : (value >= min && value <= max)
        );
        return isValid || {error: 'range', message: `Please enter a value between ${min} and ${max}`};
    };
}

function pattern(regex) {
    return function(value) {
        const skip = value === undefined || value === null;
        const isValid = skip || regex.test(value);
        return  isValid || {error: 'pattern', message: `Please enter a value which matches the specified format`}
    };
}