JavaScript the next day

First, the data type

1. Strings (String)

var mood = "Happy";

var mood = ' happy ';

2. value (number)

var age = 25;

var price = 33.25;

3. Boolean Type (Boolean)

Boolean data can only have two values of true and false;

var married = true;

var married = false;

Unlike strings, do not enclose Boolean values in quotation marks. A Boolean value of false and the string "false" are two different things.

4. Objects (object)

Date Day Object

Date objects are used to process dates and times.

Code: var today = new Date ();

var year = Today.getfullyear ();

var month = Today.getmonth () + 1;

var day = Today.getday ();

5. array Arrays (object)

The index of an array is set to 0 by default.

Defining arrays

var arr = new Array (23,23,45,56,435);

var arr2 = [23,34,546];

var arr3 = new Array ();

Arr3[0] = 234;

ARR3[1] = 234;

Ii. viewing and conversion of data types

1. View data type typeof

var mood = "Happy";

Alert (typeof mood);

Alert (typeof 95);

2. Convert to String

var married = false;

Alert (married.tostring ()); Outputs "false"

var age = 25;

Alert (age.tostring ()); Outputs "25"

3. Convert to digital

Convert parseint () to integers

Parsefloat () converted to floating point number

Cases:

var test = parseint ("Blue"); Returns NaN

var test = parseint ("1234blue"); Returns 1234

var test = parseint ("22.5"); Returns 22

var test = parsefloat ("1234blue"); Returns 1234

var test = parsefloat ("22.5"); Returns 22.5

4. determine the type of variable

A, Judge the string

typeof (a) = = ' String '

B, judging the value

typeof (a) = = ' Number '

c If it is a numeric type, but the content is not a valid number, it will show Nan, judging nan

IsNaN (a)

D, determine if the variable is empty (no variable is defined.) or define a variable but not initialize it will appear)

typeof (a) = = ' undefined '

Third, operator

1. Arithmetic operators (+-*/%)

Add, subtract, multiply, divide, and balance, where% is the remainder operation

var total = (1 + 4) * 5;

var i = 100;

var temp = (i–20)/2;

Alert ("ten" +)//return 1020;

Alert (+)//return 30;

JavaScript the next day