JavaScript Language | 30 Minute Test 3

In order to load a page, the browser must parse the contents of all script tags, which adds additional time to the page load. By minimizing the amount of JavaScript needed to render the page, and deferring parsing of unneeded JavaScript until it needs to be executed, you can reduce the initial load time of your page.

Division by zero is not an error in JavaScript: it simply returns infinity or negative infinity. There is one exception, however: zero divided by zero does not have a welldefined value, and the result of this operation is the special not-a-number value, printed as NaN.

An object creation expression creates a new object and invokes a function (called a constructor) to initialize the properties of that object. Object creation expressions are like invocation expressions except that they are prefixed with the keyword new.

The JavaScript interpreter takes no action when it executes an empty statement. The empty statement is occasionally useful when you want to create a loop that has an empty body.

If the body of a for/in loop deletes a property that has not yet been enumerated, that property will not be enumerated. If the body of the loop defines new properties on the object, those properties will generally not be enumerated.

To determine whether one object is the prototype of (or is part of the prototype chain of) another object, one should use the isPrototype() method. To find out if p is the prototype of o write p.isPrototypeOf(o).

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Functions with no return value are sometimes called procedures.

method is nothing more than a JavaScript function that is stored in a property of an object. If you have a function f and an object o, you can define a method named m of o with the following line:
o.m = f;

he above code snippet returns the value in scope.

The JSON format is intended for serialization of data structures and can handle JavaScript primitive values, arrays, and plain objects. It does not know about classes, and when serializing an object, it ignores the object’s prototype and constructor. If you call JSON.stringify() on a Range or Complex object, for example, it returns a string like {“from”:1, “to”:3} or {“r”:1, “i”:-1}.

The Date() consturctore appears in three different ways as mentioned above.

Frameworks that define module loading systems may have other methods of exporting a module’s API. There may be a provides() function for modules to register their API, or an exports object into which modules must store their API.

The subexpression /java(script)?/ matches “java” followed by the optional “script”.

The this keyword is forbidden or restricted because functions (in non-strict mode) can access the global object through this. Preventing access to the global object is one of the key purposes of any sandboxing system.

Since x is a let variable and since x is undefined, so x+1 is NaN. Thus, the above code snippet prints NaN.

When working with XML fragments, use XMLList() instead of XML():

Uncaught exceptions generate events, if any handlers are registered. Otherwise, the exception just makes Node print an error and exit.

Because packages and classes are represented as JavaScript objects, you can assign themto

Node supports the client-side timer functions set setTimeout(), setInterval(), clearTimeout(), and clearInterval().

Browsers that implement the “Web Storage” draft specification define two properties on the Window object: localStorage and sessionStorage. Both properties refer to a Storage object—a persistent associative array that maps string keys to string values.

The above code starts displaying the time when the document loads.

The setTimeout(), which registers a function to be invoked after a specified amount of time.

Nested functions are common in client-side JavaScript, because of its extensive use of event handlers.

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.

The setTimeout() method of the Window object schedules a function to run after a specified number of milliseconds elapses.

The decodeURIComponent() is a global function defined by client-side JavaScript.

The navigator property of a Window object refers to a Navigator object that contains browser vendor and version number information.

When the first argument of the open() is omitted, the about:blank is opened.

Both Text and Comment are basically strings of text, and these nodes are much like the Text nodes that represent the displaying text of a document.