Web Scripting: AJAX with JSON

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Questions and Answers

What is the primary reason for using a tool like JSON Lint when working with JSON data?

  • To validate the structure and syntax of JSON data, and to reformat it for improved readability. (correct)
  • To reduce the file size of JSON data by removing unnecessary whitespace and comments.
  • To encrypt JSON data before sending it over a network to ensure data security.
  • To automatically convert JSON data into XML format for better compatibility with older systems.

In the context of AJAX, what does XMLHttpRequest enable developers to do?

  • Bypass server-side scripting altogether, handling data processing on the client side.
  • Establish real-time, bidirectional communication channels between the client and server.
  • Create interactive user interfaces using only client-side JavaScript.
  • Issue HTTP requests (GET or POST) directly from a web browser to a web server. (correct)

What is the key difference between synchronous and asynchronous AJAX calls concerning JavaScript code execution?

  • Synchronous calls do not use XMLHttpRequest, whereas asynchronous calls do.
  • Asynchronous calls allow JavaScript code to continue execution without waiting for a response, while synchronous calls halt execution until a response is received. (correct)
  • There is no difference; both synchronous and asynchronous calls execute JavaScript code in the same manner.
  • Synchronous calls allow JavaScript code to continue execution without waiting for a response, while asynchronous calls halt execution until a response is received.

Which data format is commonly used in modern AJAX calls, superseding XML?

<p>JSON (C)</p>
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Why might a developer choose to use asynchronous AJAX calls over synchronous calls in a web application?

<p>To prevent the user interface from becoming unresponsive while waiting for a server response. (A)</p>
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Which HTTP method is typically used to send data to a server to create or update a resource?

<p>POST (B)</p>
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What is the primary advantage of using JSON for data transmission over the web?

<p>JSON's string format is easily passed through most firewalls. (B)</p>
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Consider the following JavaScript object: var product = { name: 'Laptop', price: 999.99, inStock: true }; How would you convert this object into a JSON string?

<p><code>JSON.stringify(product)</code> (C)</p>
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What is the purpose of JSON.parse() in the context of web scripting?

<p>To convert a JSON string into a JavaScript object. (B)</p>
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In the context of AJAX, what does 'asynchronous' refer to?

<p>The browser can continue processing other tasks while waiting for the server's response. (D)</p>
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Which of the following is NOT a component of a URL?

<p>Cache expiration (A)</p>
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You need to send a large amount of binary data to a server. Which HTTP method is most suitable for this task?

<p>POST (A)</p>
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Why is JSON preferred over XML in modern AJAX applications?

<p>JSON is easier to read and parse in JavaScript compared to XML. (C)</p>
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Flashcards

AJAX call speed

AJAX calls typically complete in a few seconds or less.

Synchronous AJAX call

During a synchronous AJAX call, the JavaScript code pauses execution, and waits for the server to respond before continuing.

XMLHttpRequest

XMLHttpRequest is an object that allows browsers to make HTTP requests (GET or POST) to web servers for data.

AJAX return data format

Although named XMLHttpRequest, JSON (JavaScript Object Notation) is usually the returned data format, not XML.

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JSON Lint

JSON Lint is a web tool that reformats unformatted JSON data to be more human-readable based on its structure.

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URL

The format for locating resources on the web, including protocol, internet address, and resource name.

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HTTP Methods

Commands used by HTTP to perform actions like retrieving (GET), submitting (POST), uploading (PUT), and deleting (DELETE) resources.

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HTTP GET

Requests data from a specified resource. It's the most common type of web request.

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HTTP POST

Submits data to be processed to a specified resource, with the data included in the request's body.

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JSON

A lightweight data-interchange format that's easy to read and write, and commonly used to transmit data on the web.

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JavaScript to JSON

Converting a JavaScript object into a JSON string for data transmission.

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JSON to JavaScript

Converting a JSON string back into a JavaScript object for use in client-side code.

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AJAX

A web development technique that allows web pages to update asynchronously by exchanging data with a web server behind the scenes.

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Study Notes

  • Web scripting intro - AJAX with JSON

URLs

Basic HTTP

  • HTTP commands have methods
  • GET requests a specified resource representation
  • Most web requests use HTTP GET
  • POST submits data for processing to an identified resource
  • The data is in the request body
  • PUT uploads a specified resource representation
  • DELETE deletes the named resource from a server

JSON

  • JavaScript Object Notation is an easy way to store and transport JavaScript object data as strings
  • Example JSON usage

JSON continued

  • Most Internet firewalls allow HTTP GET and POST requests by default if the data is a string
  • JSON is a good option for sending or receiving web data because it represents everything as a string
  • JSON data is easy to convert from and to JavaScript objects

Converting JSON and Javascript

  • You can convert from JavaScript objects to JSON and JSON strings back to JavaScript objects
  • JavaScript to JSON example
  • JSON to JavaScript example

AJAX

  • Asynchronous JavaScript and XML provides the ability to issue asynchronous calls from a client browser to code running on a web server and receive data in return through a callback to an event handler
  • Rarely uses XML format anymore and almost always utilizes JSON format
  • Asynchronous means that during the time between sending and receiving the request, the browser and user are free to continue working
  • Most AJAX calls take a couple of seconds or less
  • Issuing synchronous calls is possible
  • During a synchronous call, the JavaScript code will wait for an answer

Simple AJAX

  • Simple AJAX calls are possible from any browser through XMLHttpRequests
  • Every browser supports this and it lets you issue an HTTP request (usually GET or POST) to a web site
  • You are rarely expecting to get XML data back from a request
  • The data is usually JSON these days

Simple AJAX (synchronous)

  • Example function

Simple AJAX (asynchronous)

  • Example function

Working with JSON

  • JSON returned from web servers is completely unformatted and therefore difficult to interpret visually
  • The JSON Lint website can resolve this problem
  • Pasting unformatted JSON into the site display window and then reformatting based on the structure of the JSON code being analyzed is possible

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Web Scripting - Intro to AJAX and JSON PDF

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