$parser.unshift??how does this work?

Question

 link: function(scope, elm, attrs, ctrl) {         ctrl.$parsers.unshift(function(viewValue) {              scope.pwdValidLength = (viewValue && viewValue.length >= 8 ? 'valid' : undefined);             scope.pwdHasLetter = (viewValue && /[A-z]/.test(viewValue)) ? 'valid' : undefined;             scope.pwdHasNumber = (viewValue && /\d/.test(viewValue)) ? 'valid' : undefined;              if(scope.pwdValidLength && scope.pwdHasLetter && scope.pwdHasNumber) {                 ctrl.$setValidity('pwd', true);                 return viewValue;             } else {                 ctrl.$setValidity('pwd', false);                                     return undefined;             }          });     } 

http://jsfiddle.net/adamdbradley/Qdk5M/

In the above mentioned fiddle how does the password validation taking place? What does the $parser.unshift do?? and what is the use of test(viewValue).....? I have referred AngularJs main site but couldn't understand any thing... Please guide me step by step of how it is validating...

I am new to angularJS..

Answer 1

Below is a step-by-step explanation. Notice the documentation is really good: the pages on the forms and on the $parsers are the ones you're looking for.

link: function(scope, elm, attrs, ctrl) {     /**      * This function is added to the list of the $parsers.      * It will be executed the DOM (the view value) change.      * Array.unshift() put it in the beginning of the list, so      * it will be executed before all the other      */     ctrl.$parsers.unshift(function(viewValue) {          scope.pwdValidLength = (viewValue && viewValue.length >= 8 ? 'valid' : undefined); // Check the length of the string         scope.pwdHasLetter = (viewValue && /[A-z]/.test(viewValue)) ? 'valid' : undefined; // Check if the string contains letter. RegExp.test() simply returns a boolean if the string matches the regex.         scope.pwdHasNumber = (viewValue && /\d/.test(viewValue)) ? 'valid' : undefined; // Check if the string contains digit. Same remark.          if(scope.pwdValidLength && scope.pwdHasLetter && scope.pwdHasNumber) { // If all is good, then…             ctrl.$setValidity('pwd', true); // Tell the controlller that the value is valid             return viewValue; // Return this value (it will be put into the model)         } else { // … otherwise…             ctrl.$setValidity('pwd', false); // Tell the controlller that the value is invalid             return undefined; // When the value is invalid, we should return `undefined`, as asked by the documentation         }      }); }