Leak detection and vacancy filling (VII)

Leak filling （ 7、 ... and ）

standard

1.  Inline elements cannot contain block level elements ;
2.  Block level elements can contain inline elements or some block level elements ;
3. p Tags cannot contain any block level elements , Include yourself ;
4. a Tags can contain any element , But it cannot contain itself ;
5. h1、h2、h3、h4、h5、h6、p、dt Cannot contain block level elements ;
6. h5 My new label is footer, No foot;
7. h5 The label has main label 

 Pass on the overhead of the rendering phase to the computing phase .
 Use multiple layered  Canvas  Draw complex scenes .
 Don't set the drawing context frequently  font  attribute .
 Not used in animation  putImageData  Method .
 Through calculation and judgment , Avoid unnecessary drawing operations .
 Pre draw fixed content off screen  Canvas  To improve performance .
 Use  Worker  And the method of splitting tasks to avoid complex algorithms blocking animation operation 

https://blog.csdn.net/weixin_33940102/article/details/90687163?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task

'9' < '10' //false
String('a') === 'a' //true
new String('a') === 'a' //false

JS The string comparison size in is used to compare different characters of a string ASCII Code value

Object.defineProperty

const obj = {
    
	a: 1,
	b: 2
}
Object.defineProperty(obj,'c', {
    
	value: 3,
	// Restrictions on this property , If it is allowed to edit 、 Whether to allow traversal 
	//writable
	//enumerable
})

for in

for in Traversal can traverse itself and parent attributes , Cannot traverse grandpa and later properties

Event bubbling and event default

preventDefault()  Prevent event default behavior 
stopPropagation() W3C Standard to stop bubbling 
cancelBubble() ie To stop bubbling 

https://www.cnblogs.com/zhangq/p/10621413.html

let And var The difference between

1. let It's a block level scope ,var It's a function scope ;
2. let Must declare before use ,var Sure , And the result printed before the declaration is undefined;
3. let Cannot redefine with variable name ,var Sure ;
4. let、var stay for The difference in the loop ：

• • because let It's a block level scope , Use let Defined for The loop variable creates a scope each time it loops , Loop variables are local variables and will not be affected by subsequent loops ;
• • var Global variable , stay for Every change in the loop changes the global variable
• • const It is not actually guaranteed that the value of the variable cannot be changed , But the memory address that the variable points to must not be changed . For simple types of data , The value is stored in the memory address that the variable points to , So it's equivalent to a constant . But for data of composite type , The memory address pointed to by the variable holds only a pointer ,const It can only be guaranteed that the pointer is fixed , As for whether the data structure it points to is variable , You can't control .

JS Modular specification

AMD、commonJS、ES Modules
require.js yes amd The implementer of the specification