Curried validation function for JavaScript

validator.js

function validate(obj) {
  function validator(prop) {
    return function(validateFn) {
      var res = validateFn(obj[prop])
      if (!Array.isArray(res)) throw 'Validation function must return an array of arrays'
      res.forEach(arr => {
	  if (!Array.isArray(arr)) throw prop + ' validation "' + JSON.stringify(arr) + '" requires a string as first item'
          if (typeof arr[0] !== 'string') throw prop + ' validation "' + JSON.stringify(arr) + '" requires a string as first item'
      })
      var invalidation = res.find(propVal => !propVal[1])
      if (invalidation) validator.invalids[prop] = invalidation[0] || '[Undefined invalidation message]'
      return !invalidation;
    }
  }
  validator.invalids = {}
  validator.toString = function() {
    return '[invalids ' + JSON.stringify(this.invalids) + ']';
  }
  return validator;
}


validation = validate({a:11212})
validation('a')(a => [
 	['A must be higher than 5', a > 5], 
	['A must be higher than 2000', a > 200000]
])