JavaScript variables and data types

Variable

Variables in JavaScript are represented by a variable name, which is a combination of uppercase and lowercase English, numeric, $ and, and _ can only be preceded by letters, underscores, and $ . The variable name cannot be a JavaScript keyword, such as if , and while so on. Declare a variable var关键字 , for example:

var  // declaring variable a var  b = Ten;  // declaring variables and assigning values var  $a = "string";  // declaring a variable starting with a $ character var  true;  // Declare variables with _ var NULL ; var $b = undefined;

Note: variables are strictly case-sensitive.

Writing Specifications for variables:

1, Camel style--the first word lowercase, the rest of the first letter of the word capital. such as: Mynameislee

2. Underline style--the word is unified lowercase and the word is separated from the word by an underscore. such as: My_name_is_lee

Note: In the development process, you should keep the entire project consistent regardless of which writing specification is used.

Data type

in JavaScript, there are 6 types of data, namely numeric (number), Boolean (Boolean), String-type (string) 　　 , undefined, null, object type. The first four are basic data types, and Null is a special type, and object is a composite data type.

　　Number

　　JavaScript does not distinguish between integers and floating-point numbers, and is uniformly represented by number, and the following are valid number types:

// integer 1234 // floating point 1.456 // scientific notation means 1.235x1000, equivalent to 123.5 // Negative number // Nan means not a number, which is represented by Nan when the result cannot be evaluated // Infinity is infinitely large, and is represented as infinity when the value exceeds the maximum value that JavaScript can represent.

JavaScript variables and data types