How to validate forms in AngularJS

In AngularJS, form validation can be implemented using built-in directives and features provided by the framework. Here's a basic guide on how to validate forms in AngularJS:

1. Set up your form: Start by creating an HTML form using AngularJS directives. For example:

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<form name="myForm" ng-submit="submitForm()" novalidate>
    <input type="text" name="username" ng-model="user.username" required>
    <input type="email" name="email" ng-model="user.email" required>
    <button type="submit">Submit</button>
</form>

2. Use AngularJS directives for validation: AngularJS provides several directives for form validation, such as ng-model, ng-required, ng-minlength, ng-maxlength, ng-pattern, etc. In the above example, ng-model is used to bind form inputs to scope variables, and required is used to make the fields mandatory.

3. Display validation messages: AngularJS automatically adds classes to form elements based on their validation status. You can use these classes to style your form and display validation messages. For example:

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<input type="text" name="username" ng-model="user.username" required>
<div ng-show="myForm.username.$dirty && myForm.username.$invalid">
    <span ng-show="myForm.username.$error.required">Username is required.</span>
</div>

4. Disable form submission until valid: You can disable the submit button until the form is valid using the ng-disabled directive:

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<button type="submit" ng-disabled="myForm.$invalid">Submit</button>

5. Perform custom validation: You can also write custom validation functions in your controller and use them with the ng-pattern directive or by adding them to the $validators or $asyncValidators pipeline. For example:

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$scope.validatePassword = function(password) {
    return password && password.length >= 8;
};

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<input type="password" name="password" ng-model="user.password" ng-pattern="/^[a-zA-Z0-9]*$/" required>
<div ng-show="myForm.password.$error.pattern">Password should contain only letters and numbers.</div>
<div ng-show="myForm.password.$error.required">Password is required.</div>
<div ng-show="myForm.password.$error.minlength">Password is too short.</div>

By following these steps, you can implement form validation in AngularJS applications effectively.