JavaScript Language | 30 Minute Test 4

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\f is the JavaScript escape sequence that stands for Form feed (\u000C).

The operator “in” tests whether a particular property exists.

The var and function are declaration statements—they declare or define variables and functions. These statements define identifiers (variable and function names) that can be used elsewhere in your program and assign values to those identifiers.

When an exception is thrown in a jump statement, the interpreter jumps to the nearest enclosing exception handler, which may be in the same function or up the call stack in an invoking function.

The above code snippet defines a custom constructor.

The unshift() and shift() methods behave much like push() and pop(), except that they insert and remove elements from the beginning of an array rather than from the end. unshift() adds an element or elements to the beginning of the array, shifts the existing array elements up to higher indexes to make room, and returns the new length of the array. shift() removes and returns the first element of the array, shifting all subsequent elements down one place to occupy the newly vacant space at the start of the array.

The above code snippet contains nested function in which the function hypotenuse(a,b) has another function inside its scope, function square(x). The interesting thing about nested functions is their variable scoping rules. They can acceess the parameters and variables of the function (or functions) they are nested within.

You can always omit a pair of empty parentheses in a constructor invocation.

The fundamental rule of lexical scoping is that the JavaScript functions are executed using the scope chain that was in effect when they were defined.

Instances of B inherit all the instance methods of A. The class B can define its own instance methods, some of which may override methods of the same name defined by class A.

It is possible to add methods to Object.prototype, making them available on all objects. This is not recommended, however, because prior to ECMAScript5, there is no way to make these add-on methods nonenumerable, and if you add properties to Object.prototype, those properties will be reported by all for/in loops.

Rather than importing individual classes, a programmer might import the entire module to the global namespace.

When a regular expression is successfullyy matched against a target string, it is possible to extract the portions of the target string that matched any particular paranthesized subpattern. The essential purpose of parantheses in regular expressions is to define subpatterns within the complete pattern.

eval() and the Function() constructor are not allowed in any secure subset because they allow the execution of arbitrary strings of code, and these strings cannot be statically analyzed.

The above code snippet swaps the value of the two variables.

The .. operator is the descendant operator; you can use it in place of the normal . member-access operator :

var names = pt..name;

The SIGINT is a POSIX signal that generates event.

The output for the above code snippet is false as it is a writer and not a Reader.

Node defines other important globals under the process namespace.

The difference between localStorage and sessionStorage has to do with lifetime and scope: how long the data is saved for and who the data is accessible to.

The main advantage of using the src attribute is that it simplifies your HTML files by allowing you to remove large blocks of JavaScript code from them—that is, it helps keep content and behavior separate.

In client-side JavaScript, the Window object is also the global object. This means that the Window object is at the top of the scope chain and that its properties and methods are effectively global variables and global functions.

There is no object called Position.

Like Dojo, it is a large, all-encompassing library with language utilities, DOM utilities, UI widgets, and so on. There are actually two incompatible versions of YUI, known as YUI 2 and YUI 3.

setTimeout() returns a value that can be passed to clearTimeout() to cancel the execution of the scheduled function.

The replace() method is similar, but it removes the current document from the browsing history before loading the new document. When a script unconditionally loads a new document, the replace() method is often a better choice than assign().

IE supports clientInformation as a vendor-netural synonym for navigator.

The Window object serves as the global object at the top of the scope chain in client-side JavaScript.

The DOM defines a number of ways to select elements; you can query a document for an element or elements:
1.with a specified id attribute;
2.with a specified name attribute;
3.with the specified tag name;
4.with the specified CSS class or classes; or
5.matching the specified CSS selector