Introduction to JavaScript and basic syntax

Introduction to JavaScript

1, JavaScript is a scripting language, need to have a host file, his host file is an HTML file.

To use : For the sake of insurance generally written after

Three common dialog boxes:

Alert ("Put Chinese characters in this") Warning dialog box, the function is to pop up a warning dialog, such as alert ("Input error")

Confirm ("") determines the dialog box function is to pop up a selection of OK dialog box, click OK after he returns True, click Cancel to return to Flase.

Prompt ("Hint text to display"), which pops up a dialog box that allows you to enter content. For example:

Prompt ("Several numbers come in, only numbers"), click OK, return only the number, click Cancel to return null value, NULL.

Basic syntax for JavaScript

1, the basic data type:

String, Decimal, Integer, DateTime, Boolean, etc.

2, variables: are generic types of VAR, can be stored casually other types of values, can be used directly, without definition, but the customary definition. Define VAR A: All variables are defined with Var, var is a generic mutable type.

3, type conversion: can be divided into automatic conversion and casting, the general use of casting.

other types are converted to integers: parseint ();

Other types converted to decimals: parsefloat ();

In addition to determine whether it is a valid number type: IsNaN ();

is a number then returns false, not a number if it returns True, as follows:

var a=prompt ("Please enter a number")

if (a!=null)

var B=isnan (a)

if (b==flase)

Then the input of a is a number, continue to go down, if not the number is prompted to enter the error!

4: operator:

A, mathematical operator:+-*/%++--:< Plus is the plus sign when encountering a numeric type, when the type of string is encountered, the three functions are: 1, take the remainder, 2, change a number to a range, 3, and see if it is divisible. + +: Front + + shows +1, after + + equals the original value. >

B, relational operators: = = =! = > >= < <=;

C, logical operator:&& | | ！

D, other operators: + = = *=/=%=?; <x=6,y=5 so x+=y x=11, x-=y so x=1.>

5, statements: generally divided into branch statements and circular statements

(1) The branch is the IF statement

if (judging condition)

{

Satisfies the statement to be executed

}

Else

{

Statement to execute if the condition is not met

}

To loop with a for statement:

Introduction to JavaScript and basic syntax