src/rules.js
function(inputValue, ruleValue, attribute, callback) {
    var fn = this.isMissed() ? missedRuleValidator : this.fn;

    return fn.apply(this, [inputValue, ruleValue, attribute, callback]);
  }
function(inputValue, ruleValue, attribute, callback) {
    var fn = this.isMissed() ? missedRuleValidator : this.fn;

    return fn.apply(this, [inputValue, ruleValue, attribute, callback]);
  }
function ( inputValue , ruleValue , attribute , callback ) { var fn = this . isMissed ( ) ? missedRuleValidator : this . fn ; return fn . apply ( this , [ inputValue , ruleValue , attribute , callback ] ) ; }
Apply validation function

@param  {mixed} inputValue
@param  {mixed} ruleValue
@param  {string} attribute
@param  {function} callback
@return {boolean|undefined}
Apply validation function