JSON and JavaScript Basics Quiz: Test with Eval

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Questions and Answers

What is the primary purpose of a JSON file?

To convert JSON data into classes and attributes of a programming language
To send data from the server to the browser
To load data from the server or send data to it (correct)
To assign a variable to a JavaScript object

What is the role of parsers in JSON processing on the server side?

To load JSON data from the server to the browser
To convert JSON data into JavaScript objects
To process the JSON file and may even convert it into classes and attributes of the language (correct)
To send JSON data from the browser to the server

How can a JSON file be loaded from the server in JavaScript?

By including the file into the HTML page as a JavaScript.json external file
By converting the JSON file into a JavaScript object
By using the eval() function
By using the XMLHttpRequest() function or directly including the file into the HTML page (correct)

Who is the original developer of JSON?

Douglas Crockford (C) Signup and view all the answers

What is the purpose of the JavaScript eval() function in relation to JSON?

To convert JSON data into a JavaScript object (A) Signup and view all the answers

What is the ECMA standard based on?

Netscape’s JavaScript and Microsoft’s Jscript (B) Signup and view all the answers

What is the primary purpose of the same origin policy in browsers?

To prevent malicious scripts from accessing sensitive information (D) Signup and view all the answers

What determines whether a document or script is considered to be from the same origin?

The protocol and host of the URL (C) Signup and view all the answers

What is the outcome of a script accessing a document from http://www.example.com:81/dir2/other.json when the current page is http://www.example.com/dir/page.html?

Failure, because the port number is different (B) Signup and view all the answers

How can JSON be used to bypass the same origin policy?

By setting the src attribute of a script tag to a URL from another server (B) Signup and view all the answers

What is the advantage of using JSON to bypass the same origin policy?

It enables cross-domain data retrieval (B) Signup and view all the answers

In what year was the tag available in HTML, enabling the use of JSON to bypass the same origin policy?

1994 (A) Signup and view all the answers

What is the primary function of the XMLHttpRequest object?

To send HTTP requests to a server (A) Signup and view all the answers

What is the purpose of the req.readyState property in the XMLHttpRequest code?

To check the status of the HTTP request (D) Signup and view all the answers

What does the eval() function do in the JavaScript callback?

Parses JSON data and creates an object (C) Signup and view all the answers

How is the value of the 'title' field accessed in the JavaScript code?

doc.commands.title (A) Signup and view all the answers

What is the purpose of the req.send(null) method call?

To send the HTTP request to the server (B) Signup and view all the answers

What is the role of the Global Object in the context of the eval() function?

It is a function property that evaluates a string as JavaScript code (D) Signup and view all the answers

What is the purpose of the 'jsonp' dataType in jQuery.ajax()?

To load a JSON block using JSONP and add a callback parameter to the URL (C) Signup and view all the answers

What is the default callback function name used in a JSONP request?

callback (D) Signup and view all the answers

What happens to the JSON response when the 'json' dataType is specified?

It is parsed using jQuery.parseJSON before being passed to the success handler (C) Signup and view all the answers

What is the purpose of the 'dataType' option in jQuery.ajax()?

To specify the type of data expected from the server (A) Signup and view all the answers

What is the effect of specifying the 'jsonp' option in a jQuery.ajax() request?

It adds an extra '?callback=?' to the end of the URL (D) Signup and view all the answers

What is the result of parsing a JSON response when the 'json' dataType is specified?

A JavaScript object is returned (B) Signup and view all the answers

What is the main limitation of data retrieval that the JSON and Dynamic Script Tag 'Hack' aims to overcome?

Data can only be retrieved from a single domain. (D) Signup and view all the answers

What is the purpose of the 'noCacheIE' variable in the JSONScriptRequest class?

To prevent caching of requests in Internet Explorer. (A) Signup and view all the answers

What is the function of the 'buildScriptTag' method in the JSONScriptRequest class?

To create the script tag and set its attributes. (C) Signup and view all the answers

What is the purpose of the 'scriptCounter' variable in the JSONScriptRequest class?

To keep track of the number of script tags created. (D) Signup and view all the answers

What is the main functionality of the JSONScriptRequest class?

To create a dynamic script tag and set its src attribute. (C) Signup and view all the answers

What is the significance of the line 'this.scriptObj.setAttribute("src", this.fullUrl + this.noCacheIE);' in the JSONScriptRequest class?

It sets the src attribute of the script tag to a new URL. (D) Signup and view all the answers

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Study Notes

JavaScript ECMA Standard

Based on Netscape's JavaScript and Microsoft's JScript
Douglas Crockford is the original developer of JSON, now Senior JavaScript Architect at PayPal

JSON (JavaScript Object Notation)

A lightweight data interchange format
Allows loading data from a server or sending data to a server
Involves three steps: browser processing, server processing, and data exchange between them

JSON File

Can be loaded from the server or sent to the server
Can be operated upon by various programming languages (e.g., PHP, Java) using parsers
Can be converted into classes and attributes of the language

Client-Side (Browser)

JSON data is assigned to a variable, becoming an object in the program
Can be loaded from the server using XMLHttpRequest() or directly included in the HTML page

Server-Side

JSON file can be operated upon by various programming languages using parsers
Can be converted into classes and attributes of the language

Data Exchange

JSON data can be exchanged between the browser and server using XMLHttpRequest()
JSON file is sent as a text file and processed by the parser of the programming language

JSON and XMLHttpRequest

XMLHttpRequest can be used to load a JSON file from the server
XMLHttpRequest code: var req = new XMLHttpRequest(); req.open("GET", "file.json", true);
JavaScript callback: eval() parses JSON, creates an object, and assigns it to a variable

JSON eval() Function

Evaluates a string and executes it as if it was JavaScript code
Can be used to parse JSON data

Same Origin Policy

A security feature applied by browsers to client-side scripts
Prevents a document or script from getting or setting properties of a document from a different origin
Rationale: browsers should not trust content loaded from arbitrary websites

JSON Cross-Domain Hack

Uses JSON and the `

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