JS learning notes - data types

The data type of the variable determines how bits representing these values are stored in the memory of the computer .JavaScript yes A weakly typed or dynamic language . It means You don't have to declare the type of variable in advance , While the program is running , The type will be automatically determined .

When the code is running , The data type of a variable is defined by JS Engine basis = The data type of the variable value on the right , After running , Variables determine the data type .

Basic data type

JavaScript The maximum and minimum of the values in

alert(Number.MAX_VALUE) ; / / 1. 7976931348 623157e+308

alert(Number.MIN_VALUE) ; / / 5e-324

Three special values of digital type

alert(Infinity) ;
// Infinity 
alert(-Infinity) ; // - Infinity
alert (NaN) ;
// NaN

Infinity , For infinity , Greater than any number
-Infinity , For infinitesimal , Less than any number
NaN , Not a number , Represents a non numerical value

isNaN()

isNaN() Used to determine whether a variable is a non numeric type , And return a value , If it's a number , The return is false . If it's not a number , The return is true.

String escape character

String length detection

A string is made up of several characters , The number of these characters is the length of the string . Through strings length attribute You can get the length of the entire string .

String splicing

You can use... Between multiple strings + Splicing , The splicing method is character string + Any kind of = The new string after splicing

Any type added to the string will be converted into a string before splicing , And then splice it into a new string

Add the values , The characters are connected

prompt The value taken is word Haptic

typeof Determine the variable data type

console.1og(typeof str);

Data type conversion

What is data type conversion ： Is to convert a variable of one data type into another data type .

Convert to string

  Convert to digital

Convert to Boolean

Representational space 、 Negative values are converted to false , Such as "、0、NaN、null、 undefined, The rest of the values are converted to true