Tham khảo tài liệu 'tự học html và css trong 1 giờ - part 46', công nghệ thông tin, đồ họa - thiết kế - flash phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 426 LESSON 14 Introducing JavaScript Output FIGURE Values passed to functions are copies. Functions are called using the function name followed by parentheses. If you are passing arguments to a function they are included in the parentheses in a comma-separated list. Even if you re not using arguments the parentheses are still required. This is true whether you re calling a function you wrote yourself or a function that s built in to JavaScript. Data Types I ve mentioned JavaScript s type system but I haven t talked much about JavaScript data types. JavaScript supports the following types of values Strings like Teach Yourself Web Publishing . Boolean values true or false . Numbers integer or decimal. null which is used to represent an unknown or missing value. undefined the value associated with variables that have been declared but have not yet had a value assigned to them. This is the full set of primitive data types that JavaScript supports. JavaScript attempts to convert data to whatever type it needs in a given context. So if you take a Boolean value and use it in a context where a string is expected JavaScript will convert it to a string. In some cases this automatic conversion process can lead to odd results. For example if you try to use a value that s not a number in a context where a number is expected JavaScript will return a special value NaN which is short for not a number var squareRoot a string The value of squareRoot is NaN Boolean values represent a state of either true or false. You ve already seen some examples that involve boolean values. For example if statements and while loops require conditional expressions that return a Boolean value. Any JavaScript value or expression can ultimately be converted to a Boolean. The values that are treated as false are the number zero empty strings null undefined and NaN. Everything else is true. Download from The JavaScript Language 427 Arrays Arrays are lists of things. They .
