Caching And Debugging — Part 2 MCQs with Explanations

Memory leak happens when the browser for some reason doesn’t release memory from objects which are not needed any more.

Functions used in setTimeout/setInterval are referenced internally and tracked until complete, then cleaned up.

The primary purpose of a destroy function is to centralize the responsibility for cleaning up anything that the object has done that will: 1. Prevent its reference count from dropping to 0 (for example, removing problematic event listeners and callbacks and unregistering from any services). 2. Consume unnecessary CPU cycles, such as intervals or animations.

A cycle happens when two objects reference each other in such a way that both objects retain each other.

One particularly obscure way to retain an object in memory is to log it to the console.

JavaScript supports external JavaScript, in the form of .js file.

All JavaScript libraries consists of two parts: 1. The external JavaScript itself, which is simply a text file with the containing JavaScript code, saved as a .js file. 2. A “script” tag referencing the external JavaScript file and defined on the page(s) that uses the library.

is added to prefs.js when the console is automatically opened during JavaScript error.

One of the lesser known sides of external JavaScript is the ability to reference a PHP file instead of the familiar .js file.

The syntax to referencing a PHP file using external JavaScript is consistent enough with what we already know: < script type ="text/javascript" src ="myscript.php">

The PHP file is either an absolute or relative path to a PHP script instead of the usual .js file.

The global variable $HTTP_GET_VARS[] is used to get parameters.

The RegExp method test() tests for a match in its string parameter.

The function parameter “filetype” lets you tell the script what file type to expect before loading.

The method element.appendChild() is used to add the element to the desired location within the document tree.

A script is program code that doesn’t need pre-processing (e.g. compiling) before being run.

Scripting makes Web pages more dynamic) For example, without reloading a new version of a page it may allow modifications to the content of that page, or allow content to be added to or sent from that page. The former has been called DHTML (Dynamic HTML), and the latter AJAX (Asynchronous JavaScript and XML).

XMLHttpRequest makes it possible to load additional content from the Web without loading a new document, a core component of AJAX.

The Geolocation API makes the user’s current location available to browser-based applications.

WAI ARIA offers mechanisms to ensure that this additional interactivity remains usable independent of devices and disabilities.

An API may describe the ways in which a particular task is performed.

The event onAirEvent is fired when the player starts playing content being broadcasted on the channel.

The event disconnectionEvent is fired when the player disconnects from the channel, whether a result of user interaction or not.

The event ready is fired after the player is done loading. It is safe to interact with it after this event fired.

A new ad request is made every time when the method startOverlays() gets called.

The reason for avoiding the attributes property in the HTML DOM is because Attributes don’t have attributes.

The method nodeMap.setNamedItem() sets the specified attribute node (by name).

In the HTML DOM (Document Object Model), everything is a node: 1. The document itself is a document node. 2. All HTML elements are element nodes. 3. All HTML attributes are attribute nodes. 4. Text inside HTML elements are text nodes. 5. Comments are comment nodes.

In the HTML DOM, the NamedNodeMap object represents an unordered collection of an elements attribute nodes.

In the HTML DOM, the Attr object represents an HTML attribute.

Form control elements: The form object contains all the elements defined for that object such as text fields, buttons, radio buttons, and checkboxes.

The objects are organized in the hierarchy format in the HTML DOM.

All of the above mentioned are types of HTML DOM.

The Legacy DOM: This is the model which was introduced in early versions of JavaScript language. It is well supported by all browsers, but allows access only to certain key portions of documents, such as forms, form elements, and images.

Window object is the top of the hierarchy. It is the outmost element of the object hierarchy.

Form validation used to occur at the server, after the client had entered all necessary data and then pressed the Submit button.

If some of the data that had been entered by the client had been in the wrong form or was simply missing, the server would have to send all the data back to the client and request that the form be resubmitted with correct information.

First of all, the form must be checked to make sure data was entered into each form field that required it. This would need just loop through each field in the form and check for data.

The data that is entered must be checked for correct form and value. This would need to put more logic to test correctness of data.

There is no such function to validate a data) But, you can write a function with any name to validate the data.