Javascript Tutorial with Examples For Beginners (pt 1) - Variables скачать в хорошем качестве

Javascript Tutorial with Examples For Beginners (pt 1) - Variables

This is part one of a series of javascript programming tutorials for beginners about variables. JavaScript Variables JavaScript variables are containers for storing data values. In this example, x, y, and z, are variables: var x = 5; var y = 6; var z = x + y; From the example above, you can expect: x stores the value 5 y stores the value 6 z stores the value 11 JavaScript Identifiers All JavaScript variables must be identified with unique names. These unique names are called identifiers. Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume). The general rules for constructing names for variables (unique identifiers) are: Names can contain letters, digits, underscores, and dollar signs. Names must begin with a letter Names can also begin with $ and _ (but we will not use it in this tutorial) Names are case sensitive (y and Y are different variables) Reserved words (like JavaScript keywords) cannot be used as names JavaScript identifiers are case-sensitive. The Assignment Operator In JavaScript, the equal sign (=) is an "assignment" operator, not an "equal to" operator. This is different from algebra. The following does not make sense in algebra: x = x + 5 In JavaScript, however, it makes perfect sense: it assigns the value of x + 5 to x. (It calculates the value of x + 5 and puts the result into x. The value of x is incremented by 5.) The "equal to" operator is written like == in JavaScript. JavaScript Data Types JavaScript variables can hold numbers like 100 and text values like "John Doe". In programming, text values are called text strings. JavaScript can handle many types of data, but for now, just think of numbers and strings. Strings are written inside double or single quotes. Numbers are written without quotes. If you put a number in quotes, it will be treated as a text string. Example var pi = 3.14; var person = "John Doe"; var answer = 'Yes I am!'; Declaring (Creating) JavaScript Variables Creating a variable in JavaScript is called "declaring" a variable. You declare a JavaScript variable with the var keyword: var carName; After the declaration, the variable has no value. (Technically it has the value of undefined) To assign a value to the variable, use the equal sign: carName = "Volvo"; You can also assign a value to the variable when you declare it: var carName = "Volvo"; In the example below, we create a variable called carName and assign the value "Volvo" to it.