JavaScript data types

Points:

1 , typeof operator

var box=false;alert (typeof Box);

2 , Undefined type

var box;//undefined type alert (box)

3 , Null type

Alert (undefined==null)//undefined are derived from null, so they are two equal and return True

4 , Boolean type

var box =true//true is not necessarily the 1,false is not necessarily 0.javascript case-sensitive, true is not a Boolean value of alert (typeof box)

to convert a value to its corresponding Boolean value, you can use the conversion function Boolean () , which is an explicit conversion, is mandatory.

var he = ' Hehh ' var he2 = Boolean (He) alert (typeof He2)

5 , Number type

var box = 250;//decimal integer alert (box); var box =070;//octal integer, decimal output 56alert (box); var box = 3.80;//Floating-point alert (box); var box = 12.0;//automatically converts alert (box); var box = 4.12e3;//Science and Technology Act alert (box); var box =0.000000000412;//Science and Technology Act alert (box); var box =100e10000;//over range alert (box); var box = 100e10000;alert (isfinite box),//isfinite function checks for out-of-range, returns false or true/*nan, that is, non-numeric (not anumber) is a special value, This value represents a case where the operand that would have returned a numeric value did not return a value (so that no error was made). *///var box = 0/0;//nan//alert (Number.NaN)//Number.NaN Get NaN value//alert (nan+1)//any operation with Nan results in Nan//alert (Nan ==nan) Nan is not equal to itself (Nan is not equal to any value) the/*isnan () function is used to determine whether the value is Nan. The IsNaN function receives a value and attempts to convert it to a numeric value *///alert (IsNaN (NaN))//true//alert (IsNaN)//false/* There are 3 functions converting a non-numeric value to a value: Number (), parseint () and parsefloat (). Number () applies to any type, and the latter two is dedicated to converting a string to a numeric value. *///alert (number (true)); True and false//1,boolean types are converted to 1 and 0//alert respectively (numbers (25));//25, Numeric returns directly//alert (# (NULL)) ;//0, empty object returns 0//alert (number (undefined)),//nan,undefined returns Nan//alert (parseint (' 456lee '));//456 returns the integer part//alert ( parseint (' Lee456lee '))//nan, the first one that is not a value returns Nan//alert (parseint (' 12lee34lee ')//12, starting with the first value, to the last continuous numeric//alert (parseint (' 12.34 '))//12, the decimal point is not a value, remove the//alert (parseint ("))//nan, The null return Nanparsefloat () is used for floating-point numeric conversions, as is the case with parseint (), which, from the first to the non-floating-point numeric position, recognizes only a small number of decimal points and converts the scientific notation to a normal value.

6 , String type

String type some escape characters .

var box = 11;var box = True;alert (typeofbox.tostring ()); the//string,tostring () method converts the value to a string. The/*tostring () method generally does not need to be passed, but when the value is converted to a string, it can be passed the */var box = 10;alert (box.tostring ());//10, the default decimal output alert (box.tostring (2)); /1010, binary output

7 , Object type

You can also use New operator to create other types of objects. (newstring(' Xu '),new Boolean (True))

JavaScript data types