Basic JavaScript knowledge

01.Javascript several output modes

Document.wrte (); Document Print output

Console.log (); Console output

Console.warn (); Console Alerts

Console.error (); Console error prompt

Alert (); pop-up windows, rarely used, poor user experience

02. Three elements of the event

Event Source Event Event Handler

Event source. Event =function () {event handler};

Common event Description

• OnClick Mouse click
• OnDblClick Mouse Double-click
• onkeyup triggers when a key of the keyboard is pressed and released
• OnChange the options in the text content or drop-down menu change
• Onfocus gets focus, indicates text box, etc. get mouse cursor
• Onblur loses focus, indicates that the text box loses the mouse cursor
• onmouseover mouse hover, that is, the mouse over the picture, etc.
• onmouseout mouse removal, that is, to leave the image and other areas
• OnLoad Web page document Load event
• OnUnload when you close a webpage
• OnSubmit Form Submission Events
• OnReset when resetting the form

03. Hide Style

Display:none Display:block; The meaning of the display

Visibility:hidden; Visibility:visible the meaning of the display

Display Hide not occupying position

Visibility:hidden hide occupy position suspended pay attention

Overflow:hidden; Hide the excess part

04 images have been switched

var Pic=document.getelementbyid ("pic");

Pic.onmouseover=function () {

Pic.src= "Images/02.jpg";

}

Pic.onmouseout=function () {

Pic.src= "Images/01.jpg"; Style is added style,src is a property, do not need

}

The writing position of 04.js

1. in-line

<button onclick= "alert (' Hello ')" > click me </button>

2. Built-in

<script type= "Text/javascript" > </script>//Anywhere

3. External-linked

<script type= "Text/javascript" src= "xx.js" ></script>//There's nothing inside.

Data type

Js data types are divided into:

Character-type numeric Boolean type null undefined

Js is a kind of weak data type.

Var Aa = 10;

Var aa:int = 10;

Js variable you give what value, he is what data type.

Character type (string)

String

Convert to Character type:

1. Use "" (double quotes)

The quotes are all character types.

2. Using string (); Convert to Character type

Boolean Type (Boolean)

True and false for two values right and wrong

The data type is converted to a Boolean type:

1. Use!!

console. log (typeof!!) NUM);

2. Using the Boolean ()

False, undefined, null, 0, "" is false

True, 1, "somestring", "[Object] is true"

Numeric type

Var num = 10

A value preceded by 0 indicates octal

Var num = 020;

0*80+2*81 = 16

Value preceded by 0x for hexadecimal

var result = 0xb; 11

Convert to Numeric type:

1. Use-*/both can be converted

2 Using number ()

parseint () parsefloat ()

parseint (value, binary);      

parseint (110,2)

Represents 2 binary Bar 10 This 2 binary conversion to 10 binary

0*20+1*21 + 1*22 = 6

1.var a= "15.15abc", b= ' 10.15 ', c= ' 10.0abc ';

Alert (parseint (a) +number (b) +parsefloat (c));

Null undefined

Null empty has no value.

Undefined undefined should have a value, but not given.

Null ""

Basic JavaScript knowledge