[AngularJS] $scope.$watch

/**

 * Created by Answer1215 on 11/13/2014.

 */

function MainCtrl($scope){

    function isLongEnough (pwd) {

        return pwd.length > 4;

    }

    function hasNumbers (pwd) {

        return /[0-9]/.test(pwd);

    }

    this.watchPwd =  function(newVal, oldVal){

        //first init, you might got undefined

        if (!newVal) return;

        $scope.reqs = [];

        if (!isLongEnough(newVal)) {

            $scope.reqs.push('Too short');

        }

        if (!hasNumbers(newVal)) {

            $scope.reqs.push('Must include numbers');

        }

        $scope.showReqs = $scope.reqs.length;

    }

    //user.password is a string

    //user is an object

    $scope.$watch('user.password',this.watchPwd);

    //$watch can accept the third argument, once add it, angularJS

    //will do lose value checking instead of reference checking, it's quite

    //expensive

    //in all $watch is expensive, use ng-change if you can

   // $scope.$watch('user.password',this.watchPwd, true);

}

angular.module('app',[])

    .controller('MainCtrl', MainCtrl);

$watch can accept the third arguement, once set it as true:

$scope.$watch('user.password',this.watchPwd, true);

AngularJS will do lose value checking instead of reference checking, it is quite expensive.

For best pratise: avoid using $watch as much as you can, instead using ng-change.

<input ng-model="myModel" ng-change="callback">

<!--

  $scope.callback = function () {

    // go

  };

-->

<!DOCTYPE html>

<html ng-app="app">

<head lang="en">

    <meta charset="UTF-8">

    <title>$watch</title>

    <script src="bower_components/angular/angular.min.js"></script>

    <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css"/>

    <style type="text/css">

        .panel {

            width: 70%;

            margin: 30px auto;

        }

    </style>

</head>

<body ng-controller="MainCtrl">

<div class="panel panel-primary">

    <div class="panel-heading">

        <h3 class="panel-title">Create Account</h3>

    </div>

    <div class="panel-body">

        <form role="form">

            <div class="form-group">

                <label for="eml">Email address</label>

                <input id="eml"

                        type="email"

                        class="form-control"

                        placeholder="Email address"

                        ng-model="user.email"/>

            </div>

            <div class="form-group">

                <label for="pwd">Password</label>

                <input id="pwd"

                       type="password"

                       class="form-control"

                       placeholder="Password"

                       ng-model="user.password" />

            </div>

            <button type="submit" class="btn btn-default">Submit</button>

        </form>

    </div>

</div>

<div class="panel panel-danger" ng-show="showReqs">

    <div class="panel-heading">

        <h3 class="panel-title">Password Requirement</h3>

    </div>

    <div class="panel-body">

        <ul>

            <li ng-repeat="req in reqs">{{req}}</li>

        </ul>

    </div>

</div>

<script src="app.js"></script>

</body>

</html>

巴特西

[AngularJS] $scope.$watch

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