(Music) Hello. Welcome to The JavaScript language, Overview and Syntax. After watching this video, you will be able to describe JavaScript primitives and objects. JavaScript is a scripting language that is derived from the ECMAScript standard and originally designed to run on the Netscape Navigator browser. Virtually all browsers now support JavaScript. Although the name “Java” appears in the word “JavaScript”, the two languages are not related. When a JavaScript interpreter is embedded in a browser, the result is the ability to create dynamic web pages: JavaScript adds behavior to otherwise static web content. The content of a web page can be dynamically changed with the scripting capability of the JavaScript interpreter. JavaScript code acts on the document object model that the web browser generates. One of the ways that server programming and browser scripting work together is in an architecture that is called Ajax, or Asynchronous JavaScript and XML. The term "Ajax" encompasses more than asynchronous server calls through JavaScript and XML. Ajax represents a series of techniques that provide richer, interactive web applications through HTML, JavaScript, Cascading style sheets, and modifying the web page through the Document Object Model. Nowadays, JSON is commonly used instead of XML. In JavaScript, there are five primitive types that are associated with various primitive values: Number: All numbers, such as 0 or 3.1412, String: All strings, such as “Hello World”, Boolean: The values true or false, Null: The value null. Undefined: The value undefined, since a data type has not been assigned or the variable does not exist. All other non-primitive data types are objects. The number primitive represents both integer and floating point values, the value NaN (not a number), and Infinity. Integers can be coded as base 10 (decimal), base 8 (octal), or base 16 (hexadecimal) values. The integer literal 16 in decimal, 020 in octal, and 0x10 in hexadecimal all have the same value. All numbers in JavaScript are represented internally as double precision or 64 bit floating point numbers. JavaScript strings are delimited by either double or single quotation marks. There is no behavior or methods that are associated with primitive data types. The primitive types number, string, and boolean can be wrapped by their object counterparts. Wrapper objects have the same name as the primitive type, except they start with an uppercase letter. Like most object-oriented programming languages, JavaScript provides built-in ways to convert between these wrapper objects and primitive values. The wrapper objects use special methods such as the valueOf and toString methods to convert between objects and primitive literals. The typeof keyword in JavaScript is used to find out the data type of the supplied operand. Notice how strings created without the new keyword have a type of string. The keyword new is used to create the String wrapper object. This object can be converted to a primitive string type by calling the valueOf function on the object wrapper class. Arrays are specialized collection objects that aid the programmer in the storage and retrieval of data by indexed keys. Arrays use a zero-based indexing scheme, meaning that the first element of an array has an index of zero. Arrays grow or shrink dynamically by adding or removing elements. The length property holds the number of elements that occur in the array. Arrays can be declared by using either an array constructor or an array literal. When declaring an array with a constructor, you use the new array keywords and specify the array elements as parameters of the new array. Array literals are created by declaring the array elements within square brackets. You then assign the array to a variable, as seen in the last example on the slide. The Date object is a specialized object that is used to hold the date and time. The constructor for a date object is in the format: new Date ([with optional parameters]). If you create a Date object without any parameters, JavaScript returns an object that contains the current local date and time. If you send this date object to the console or try to display the date object on a web page, JavaScript automatically applies a toString method to the object. The result that is displayed is a string version of the date as shown on this slide. You can also create new dates by passing parameters to the new Date function. Examples on the slide show how either string or numeric values can be used for the date parameters when creating new date objects. As with other object-oriented languages, JavaScript creates error object instances when an exception occurs. The error object instance includes two properties that contain information about the error: The message property contains a description about the error. The name property identifies the type of error such as a RangeError. A RangeError is an error instance that is created when a numeric value or parameter is outside of its valid range. Besides a generic error, there are six other core errors types in JavaScript, three of which are shown on the slide. The other three are EvalError, ReferenceError, and SyntaxError. The Error object can be extended to create custom error types. The last line of the slide shows the creation of a generic error object with a custom error message in the parameter field. In this video, you learned: JavaScript is a scripting language that adds behavior to otherwise static web content. Primitives are values, and have no properties or methods. Examples of primitives include: number, string, boolean, null, and undefined. Wrapper objects allow objects of corresponding primitive data types to be created. Wrapper objects can store a primitive value and provide methods with which to process it. Wrapper objects have the same name as the primitive type, but they begin with a capital letter to differentiate them from the primitive data type itself. Some examples of wrapper objects are array, date, and error objects.
