JavaScript - dynamic computer programming language презентация

Agenda Basic Information Including JS Code into HTML Comments Variables Data Types Type Casting

Basic Information

Basic information JavaScript - dynamic computer programming language. It is most commonly used as part of web browsers, whose implementations allow client-side to interact with the user, control the browser and asynchronously communicate with server-side. JavaScript syntax was influenced by C.

Basic information JS take many names and naming conventions from Java, but the two languages are otherwise unrelated and have very different semantics. JavaScript is a prototype-based scripting language with dynamic typing. JS supported object-oriented, imperative and functional programming styles.

Including JS Code into HTML

Including of JavaScript Exist three ways to include script into HTML page: Inline in HTML Inside tag <script> In separate file

Inline including Unfortunately, this is the worst solution. Holistic code will be broken into smaller parts. Such parts are difficult to test and maintain. :(

Inside tag <script> Sometimes it makes sense. But in the general case, page size will be increased and, as a result, its performance reduced.

In separate file This is the best way. Code is holistic. It’s easy to test and maintain. In addition, separated files are cached by the browser. This improves performance. :)

Comments

Comments Comments - part of the program text which will be ignored by language interpreter The /* characters, followed by any sequence of characters (including new lines), followed by the */ characters. The // characters, followed by any sequence of characters, but only in current line. Therefore, it is commonly called a "single-line comment."

Variables

Variables Variable – symbolic name associated with a value and whose associated value may be changed.

Declaration and initialization var – special keyword for declaration of variables In JavaScript

Global and local JavaScript has two types of variables: global - exist in memory and is available at all times of the program. In JS it's a variables of page. local - exist in memory and is available only in block when variable is defined. In JS it's defined in function variables.

Data Types

Data types JavaScript have 6 base data types: Number – scalar type for integer and real digits Boolean – scalar type for logical values String – special type for work with text information Undefined – special type for uninitialized variables Null – special type for "cleaning" of variables Object – complex type for service and user needs

Number, Boolean and String

Null and Undefined And Object type… but it will be reviewed in future :)

Type Casting

Type casting

Type casting Exist two types of casting:

Type casting Base rules of typing casting: All scalar types try to convert itself to largest scalar type: Boolean to Number, Number to String. If Boolean converted to String it at first converted to Number and after them Number to String. In mathematical operations (excluding +) String should be converted to Number. Null and Undefined converted to String as “null” and “undefined”, and to Number as a 0 and NaN