JavaScript History and Versions
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JavaScript History and Versions

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Questions and Answers

What will be the result of the expression '3 * 2'?

  • 6 (correct)
  • 1
  • 3
  • 5

    • Which operator would you use to increment a variable by 1?

  • +=
  • +
  • --
  • ++ (correct)

    • What is the standardized version of JavaScript called?

  • ECMAScript (correct)
  • JScript
  • JavaScript Standard Edition
  • NetscapeScript

    • What is the output of the expression '3 + 2'?

    <p>5</p> Signup and view all the answers

    What is the primary reason Netscape's JavaScript had to be standardized?

    <p>To avoid trademark issues</p> Signup and view all the answers

    What does the expression 'x < y' evaluate to if x = 2 and y = 3?

    <p>true</p> Signup and view all the answers

    Which version of ECMAScript was in stable use across web browsers for about a decade?

    <p>ECMAScript 3</p> Signup and view all the answers

    What is the output of the expression 'count *= 3' if count is initially 2?

    <p>6</p> Signup and view all the answers

    What is the version number of the V8 JavaScript engine mentioned?

    <p>3.0</p> Signup and view all the answers

    Which JavaScript version corresponds to ECMAScript 3?

    <p>JavaScript 1.5</p> Signup and view all the answers

    What is the result of 'false == (x > y)' when x = 2 and y = 3?

    <p>true</p> Signup and view all the answers

    Which version of ECMAScript was developed but never released due to being too ambitious?

    <p>ECMAScript 4</p> Signup and view all the answers

    What is the result of the expression '!(x == y)' when x = 2 and y = 3?

    <p>true</p> Signup and view all the answers

    Which of the following is a correct way to perform subtraction in JavaScript?

    <p>3 - 2</p> Signup and view all the answers

    What is Microsoft's implementation of JavaScript formally known as?

    <p>JScript</p> Signup and view all the answers

    Which version of ECMAScript is mentioned as being the most recent at the time of writing?

    <p>ECMAScript 5</p> Signup and view all the answers

    What happens when the browser supports localStorage and there is stored data?

    <p>The input fields are populated with stored values.</p> Signup and view all the answers

    What is the purpose of the getLenders function?

    <p>To return a list of lenders using a server-side service.</p> Signup and view all the answers

    Which object is used to make an asynchronous HTTP request in the getLenders function?

    <p>XMLHttpRequest</p> Signup and view all the answers

    What is the first step when the getLenders function is called?

    <p>Check if XMLHttpRequest is supported by the browser.</p> Signup and view all the answers

    What does the function do if the browser does not support XMLHttpRequest?

    <p>It exits the function and does nothing.</p> Signup and view all the answers

    What format does the getLenders function use to send user data to the server?

    <p>Query parameters in a URL</p> Signup and view all the answers

    How is the user input encoded in the URL for the request?

    <p>Using encodeURIComponent</p> Signup and view all the answers

    What is indicated by the comment about 'asynchronous programming' in the context of client-side JavaScript?

    <p>Events can occur after the function has returned.</p> Signup and view all the answers

    What distinguishes an expression from a statement in programming?

    <p>Expressions compute a value and do not alter the program state.</p> Signup and view all the answers

    What is a characteristic of a function in JavaScript?

    <p>A function is a named and parameterized block of code.</p> Signup and view all the answers

    How is a method defined in JavaScript?

    <p>As a variable assigned a function that operates on data.</p> Signup and view all the answers

    What does the 'this' keyword refer to within a method in JavaScript?

    <p>The object on which the method is defined.</p> Signup and view all the answers

    In the provided example, what does the plus1 function return when invoked with an argument of 3?

    <p>4</p> Signup and view all the answers

    What happens when you invoke square(plus1(y)) if y is 3?

    <p>The result will be 16.</p> Signup and view all the answers

    What is the primary purpose of control structures in programming?

    <p>To alter the program state based on conditions.</p> Signup and view all the answers

    What does the push() method do when invoked on an array in JavaScript?

    <p>Adds elements to the end of the array.</p> Signup and view all the answers

    What does the value null convert to when changed to a Boolean?

    <p>false</p> Signup and view all the answers

    Which of the following values converts to NaN when turned into a number?

    <p>'one'</p> Signup and view all the answers

    What is the numeric conversion result of the string '1.2'?

    <p>1.2</p> Signup and view all the answers

    How does the value {} (any object) convert when treated as a string?

    <p>[object Object]</p> Signup and view all the answers

    What does the value false convert to when coerced into a number?

    <p>0</p> Signup and view all the answers

    Which of the following values converts to true when evaluated as a Boolean?

    <p>any empty array []</p> Signup and view all the answers

    What happens when attempting to convert undefined to a number?

    <p>NaN</p> Signup and view all the answers

    Study Notes

    JavaScript History and Versions

    • JavaScript was initially developed at Netscape.
    • “JavaScript” is a trademark licensed by Sun Microsystems (now Oracle) for Netscape’s (now Mozilla’s) implementation.
    • The standardized version of the language is called ‘ECMAScript’ due to trademark restrictions.
    • Microsoft’s version of JavaScript is called ‘JScript.’
    • Generally, the language is referred to as JavaScript.
    • This book uses ‘ECMAScript’ to refer to the language standard.

    Major ECMAScript Versions

    • All web browsers currently implement version 3 of the ECMAScript standard (ES3).
    • A new version of the language, ECMAScript version 5 (ES5), has been defined and is being adopted by browsers.
    • This book covers both ES3 and ES5 features.

    JavaScript Version Numbers

    • ECMAScript versions 3 and 5 are relevant for the language itself.
    • Version 4 of ECMAScript was developed but never released.
    • Mozilla uses its own version numbers, starting with 1.5, which is essentially ECMAScript 3.
    • Mozilla’s later versions include nonstandard language extensions.
    • JavaScript interpreters have their own version numbers. For example, Google’s V8 interpreter is currently at version 3.0.

    Arithmetic Operators

    • Operators like addition (+), subtraction (-), multiplication (*), and division (/) are common.
    • Shorthand arithmetic operators (++, --, +=, *=) provide concise ways to increment, decrement, and modify values.

    Equality and Relational Operators

    • Operators like == (equality), != (inequality), < (less than), > (greater than), <= (less than or equal), >= (greater than or equal) compare values.
    • They return true or false based on the comparison result.
    • String comparisons use alphabetical order.

    Logical Operators

    • Logical operators combine or invert boolean values.
    • && (AND) returns true only if both operands are true.
    • || (OR) returns true if at least one operand is true.
    • ! (NOT) inverts a boolean value.

    Functions

    • Functions are blocks of code that can be invoked repeatedly.
    • Defined using the function keyword, a name, and parameters enclosed in parentheses.
    • Functions can return values.
    • Can be assigned to variables.
    • When functions are assigned to object properties, they are called ‘methods.’

    Methods and Objects

    • All JavaScript objects have built-in methods (e.g., push() for arrays).
    • Methods can be defined for custom objects.
    • The this keyword refers to the object on which the method is defined.

    Client-Side JavaScript and XMLHttpRequest

    • JavaScript code can interact with the server using XMLHttpRequest objects.
    • Functions can be used to fetch data from URLs.
    • Asynchronous programming (e.g., handling server responses) is common in client-side JavaScript.

    JavaScript Type Conversions

    • JavaScript automatically converts values between data types (e.g., strings, numbers, booleans, objects).
    • Conversion to string is well-defined for all primitive values.
    • Conversion to boolean follows specific rules (e.g., true converts to 1, false and the empty string "" convert to 0).
    • Number conversions are complex, with strings that can be parsed as numbers converting to those numbers.

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    Related Documents

    JavaScript: The Definitive Guide PDF

    Description

    Explore the origins and developments of JavaScript, from its initial creation at Netscape to its various versions like ECMAScript. Understand the differences between ES3 and ES5 and the reason why some versions, like ES4, were never released. This quiz will enhance your knowledge of the JavaScript language standard.

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