JavaScript Learning Notes data types and variables

The three most basic data types in javascript: numeric, Text, Boolean.

Numeric types are divided into integers and floating-point numbers.

Text type is a character or string, placed in double quotation marks "" or single quotation mark "can be, if the string contains quotation marks, you can use the escape character, \ ' \", the other common escape characters: \ \ backslash, \ n line break, \ r carriage, \ t tab tab,\b backspace character, \f page break, \ XNN nn is a hexadecimal number that represents one character in the Latin-1 character set.

The Boolean type is divided into true and false.

The basic operators in JavaScript, including the self-increment decrement operators, are similar to C.

If you want to concatenate strings, use the + sign directly, for example:

var constring= "Hello" + "" + "world";

If you concatenate values and strings with +, JavaScript automatically converts the numeric values into strings.

A function that can convert a string to a numeric value:

parseint () and parsefloat ()

The two functions parse whether each character of the string is a valid number, and if so, return the corresponding value, otherwise stop the conversion and return the previously converted value.

For example: parseint ("123abc"), the statement returns 123, and stops when the letter A is resolved.

If you convert a string that does not contain any numbers, you get the result Nan, which means not a number.

There is a function isNaN () that checks whether a value is Nan and returns True and false.

Definition of the array:

 var  myarray = new   Array ();  var   Myarray;myarray  = new   Array ();  var  myarray = new  Array (6); var  myarray = new  Array ("Hello", 345, " Paul ", 1234 var  myarray = new   Array (); myarray[ 0] = "Hello" ;myarray[ 1 ] = 345;myarray[ 2] = "Paul" ;myarray[ 3] = 1234; 

To create a multidimensional array, declare the elements of one array again as an array.

JavaScript Learning Notes data types and variables