Custom jquery-validation handling for check boxes must equal true

checkbox-validation.js

window.onload = () => {
  /*
      Custom jquery-validation handling for check boxes must equal true
      Decorate C# model bool properties with
      [Range(typeof(bool), 'true', 'true', ErrorMessage = 'Add your error message')]
      to make their corresponding checkbox validate to 'must equal true'
  */
  var defaultRangeValidator = $.validator.methods.range;
  $.validator.methods.range = function (value, element, param) {
      if (element.type === 'checkbox') {
          // if it's a checkbox return true if it is checked
          return element.checked;
      } else {
          // otherwise run the default validation function
          return defaultRangeValidator.call(this, value, element, param);
      }
  }
};