Leak detection and vacancy filling (IV)

XMLHttpRequest object

XMLHttpRequest Object's readyState And status The meaning of several status codes :
readyState There are five states ：

1. 0 ( uninitialized )： (XMLHttpRequest) Object created , But it's not called yet open() Method ;
2. 1 ( load )： Has called open() Method , But the request has not been sent ;
3. 2 ( Loading completed )： The request has been sent ;
4. 3 ( Interaction )： Partial response data can be received ;
5. 4 ( complete )： All data has been received , And the connection has been closed .

status It is actually a kind of auxiliary state judgment , It's just status It's more about the state judgment of the server side . About status, Only a few commonly used ：
6. 1xx—— Information class , To indicate receipt of Web Browser request , In further processing . Such as ,100： Customer must continue to request ;101： The client requires the server to convert according to the request HTTP Protocol version
7. 2xx—— success , Indicates that the user request was received correctly , Understanding and handling . for example ,200：OK;201： Prompt for new documents URL
8. 3xx—— Redirect , The request was unsuccessful , The customer has to take further action . Such as ,300： The requested resources can be obtained in many places ;301： Delete request data
9. 4xx—— Client error , Indicates that the request submitted by the client has an error . Such as ,404：NOT Found, It means that the document referenced in the request does not exist .
10. 5xx—— Server error , Indicates that the server cannot complete the processing of the request . Such as ,500, The server generated an internal error

Be careful ：status Property returns the status code , No, statusCode This attribute

dl list

dl The tag defines a list of definitions , among dt(“definition title”, Define the title ) and dd(“definition description”, Definition description ) Created .

<dl>
	<dt></dt>
	<dd></dd>
</dl>

Semantic understanding

• div The element itself has no semantics , But it can be combined with class、title、lang Property to represent a set of semantic content
• time Element is used to represent time 、address Element is used to represent the address
• fieldset Tags group form controls ,legend The label is fieldset Label definition title , Use two labels together

<fieldset>
	<legend></legend>
</fieldset>

Data serialization technology

• JSON
• Property List
• Protocol Buffer

noscript label

Define the alternative content when the script is not executed

h5 You can omit the element of the end tag

1. dd
2. dt
3. li
4. p
5. optgroup： hold option Put together

<select>
	<optgroup label="label1">
		<option></option>
		<option></option>
	</optgroup>
	<optgroup label="label2">
		<option></option>
		<option></option>
	</optgroup>
</select>
//label must , Equivalent to category name 

6. option
7. rt
8. rp
9. thead
10. tfoot
11. tr
12. td
13. th

Object.keys()

Returns an array of enumerable properties of a given object

function a(a)
{
    
  a^=(1<<4)-1;
   return a;
}
a(10); //5

<< Move left , First into 2 Base number ,1 by 01, Then move left 4 position , become 010000, Turn it into 10 Base number ,10000( Binary system ) = 16( Decimal system ).
a^=16-1=15
a=a^15 = 10^15
^ Exclusive or operation ：10 Binary system 00001010,15 Binary system 00001111
00000101 To decimal ：5
Bitwise exclusive or operation , A fellow 1 Or both 0 take 0, Different take 1

Browser object

Objects related to browsing lists ：
History Object contains user （ In the browser window ） Visited URL
Location Object contains information about the current URL Information about
Window Object represents an open window in the browser
Navigator Object contains information about the browser

iframe Usage scenarios of

1. ajax Upload files .
2. Resource loading ： Load other website content , for example google advertisement , Website traffic analysis .
3. To upload pictures , Avoid refreshing the current page ： When uploading pictures , no need flash Achieve no refresh .
4. When accessing across domains, you can use iframe, Use iframe Request resources under different domain names .
5. Left fixed right adaptive layout
6. Share with pages under third-party domain names cookie

ID regular expression ：

https://www.cnblogs.com/ifat3/p/8570062.html

JavaScript It's single threaded , The browser implements asynchronous operation , Whole js Programs are event driven , Each event will be bound with the corresponding callback function （Ajax Asynchronous execution calls are based on Event and callback）

CSS Percentage reference question

• The element that refers to the width of the parent element ：padding margin width text-indent
• An element that refers to the height of the parent element ：height
• Refer to the parent element attribute ：font-size line-height
• special ： Relative positioning ,top(bottom) left(right) It refers to the height and width of the content area of the parent element , When absolute positioning, it refers to the nearest positioning element, including padding Height and width of

html5 Manual semantic tags ：

1. article
2. section
3. aside
4. hgroup
5. header
6. footer
7. nav
8. time
9. mark
10. figure： Define independent stream content , For example, the picture 、 Photographers 、 Picture information is written in a figure Next
11. figcaption： Definition figure The title of the element
12. contextmenu+menu

Trigger reflow Reflux conditions

1. Font size changes （font）
2. Window size changes （scroll）
3. Style sheet add or delete
4. JS change DOM Elements
5. hover action
6. Position calculation
7. User input
8. Change style properties
9. width/height/border/margin/padding Modification of
10. Read some properties of an element （offsetLeft、offsetTop、offsetHeight、offsetWidth、scrollTop/Left/Width/Height、clientTop/Left/Width/Height、getComputedStyle()、currentStyle(in IE))

Be careful ：visibility Preserve physical space , Even if it's set visibility:hidden But the page structure has not changed , All will not trigger reflow