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Give an example of when use an isolated scope in Angular.js?
An example of when to use an isolated scope in Angular.js is when creating a custom directive that needs to manipulate data in a specific way, without affecting the parent scope.
For example, let’s say we have a directive called “my-item” that displays information about a single item in a list. The directive has the following HTML:
<my-item name="item.name" price="item.price"></my-item>In this case, the “name” and “price” attributes are passed to the directive from the parent scope, and the directive displays this information in a specific way.
To create an isolated scope for this directive, we can modify its definition to include a scope option:
app.directive("myItem", function() {
return {
restrict: "E",
scope: {
name: "@",
price: "="
},
template: "<div>Name: {{name}}</div><div>Price: <input type='number' ng-model='price'></div>"
};
});In this example, the “scope” option defines an isolated scope for the directive, with two properties: “name” and “price”. The “@” symbol indicates that the “name” property is a string that is passed from the parent scope, while the “=” symbol indicates that the “price” property is a two-way binding with the parent scope.
The directive’s template then uses these properties to display the name and price of the item. The “name” property is displayed as text, while the “price” property is displayed as an input field that can be edited by the user. Any changes made to the “price” property in the directive will also affect the parent scope, thanks to the two-way binding.
Using an isolated scope in this example allows us to create a reusable and modular directive that can be easily customized for different use cases, without affecting the parent scope.
How does Angular.js handle changes to the model and updates to the view?
Angular.js uses a two-way data binding system to handle changes to the model and updates to the view.
When a user interacts with an Angular.js application, such as by entering data into a form or clicking a button, the model data is automatically updated to reflect the change. This is done through a process called data binding, which is a way of synchronizing the model data with the view.
Angular.js uses a special type of data binding called two-way data binding, which means that changes to the model are automatically reflected in the view, and vice versa. This makes it easy to create dynamic, interactive applications without having to manually update the view.
Here’s an example of how two-way data binding works in Angular.js:
The user enters data into an input field on the page.
The input field is bound to a property in the Angular.js model using the ng-model directive.
As soon as the user enters data into the field, the model is automatically updated to reflect the change.
The view is then automatically updated to display the new data, thanks to the two-way data binding.
If the user makes further changes to the input field, the model is updated again, and the view is updated to reflect the new data.
This process works seamlessly in Angular.js, allowing for a smooth and responsive user experience. It also makes it easy to keep the model and view in sync, as any changes made to one are automatically reflected in the other.
Explain the concept of digest cycle in Angular.js?
In Angular.js, the digest cycle is a mechanism that synchronizes the model with the view. It is responsible for detecting changes to the model and updating the view accordingly.
During the digest cycle, Angular.js checks all the properties of the $scope object and compares them to their previous values. If any changes are detected, Angular.js updates the view to reflect these changes.
The digest cycle is triggered by a variety of events, such as user interactions with the page, timers, and AJAX requests. These events cause Angular.js to run a digest cycle, which checks for any changes to the model and updates the view as necessary.
The digest cycle runs repeatedly until all changes to the model have been synchronized with the view. This means that if a change to the model triggers another change, the digest cycle will run again to ensure that all changes are properly reflected in the view.
The digest cycle can be thought of as a loop that runs continuously in the background of an Angular.js application, checking for changes and updating the view as necessary. It is an essential part of the Angular.js framework, as it ensures that the model and view are always in sync, providing a seamless and responsive user experience.
How does Angular.js handle exceptions and errors during data binding?
In Angular.js, when an error occurs during data binding, such as a reference to an undefined property, it is caught and logged to the console by default. Angular.js provides a number of tools and features to help developers handle and debug these errors.
One of the key features of Angular.js is its dependency injection system, which allows developers to easily swap out components and services in their applications. This system also makes it easy to handle exceptions and errors during data binding.
Angular.js provides a number of built-in directives and services that can be used to handle exceptions and errors. For example, the ng-if directive can be used to conditionally display content based on the state of the model. If an error occurs during data binding, the ng-if directive can be used to display an error message to the user.
Another tool provided by Angular.js for handling exceptions and errors is the $exceptionHandler service. This service can be used to intercept and handle any exceptions that occur during data binding. Developers can define their own exception handling logic, such as logging the error to a server or displaying a custom error message to the user.
In addition to these tools and features, Angular.js provides a robust debugging system that allows developers to quickly and easily identify and fix errors in their applications. The framework provides detailed error messages and stack traces, making it easy to track down the source of the error.
Overall, Angular.js provides a number of powerful tools and features for handling exceptions and errors during data binding, making it easy for developers to build robust and reliable applications.
How to use the $watch and $apply methods in Angular.js to manage changes to the scope?
In Angular.js, the $watch method is used to monitor changes to a specific property on the $scope object. It takes two parameters: the first is a function that returns the value to be watched, and the second is a function that is called whenever the value changes. Here’s an example:
$scope.$watch('propertyName', function(newValue, oldValue) {
// Do something when the value changes
});In this example, ‘propertyName’ is the name of the property on the $scope object that we want to watch for changes. The second parameter is a function that takes two parameters: the new value of the property and the old value of the property. This function is called whenever the value of ‘propertyName’ changes.
The $apply method is used to manually trigger a digest cycle in Angular.js. This is useful when changes to the $scope object are made outside of Angular’s normal data binding mechanisms, such as when working with third-party libraries or native JavaScript code. Here’s an example:
$scope.$apply(function() {
// Update the $scope object
});In this example, we pass a function to the $apply method that updates the $scope object. When this function is executed, Angular.js will run a digest cycle to synchronize the changes with the view.
In summary, the $watch method is used to monitor changes to a specific property on the $scope object, while the $apply method is used to manually trigger a digest cycle when changes to the $scope object are made outside of Angular’s normal data binding mechanisms. These methods are essential for managing changes to the $scope object in Angular.js.
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