The difference between $ ("# air") and document. getelementbyid ("Air") in jquery

I have never noticed that $ ("# air") in jquery is the same thing as document. getelementbyid ("Air"). It refers to the same thing. Write a canvasProgramThe two are different.

Directly use alert () to show what the two methods actually obtain.CodeAs follows:

 <!  Doctype html  >  
  <  Html  >  
  <  Head  >  
  < Meta  Charset  = "UTF-8"  >  
  <  Title  >  Air  </  Title  >  
  <  Link  Href  = "CSS/index.css" REL  = "Stylesheet"  Type  = "Text/CSS"  >  
  <  Script  SRC  = "JS/jquery-1.4.2.min.js"  Type  = "Text/JavaScript"  > </  Script  >  
  </ Head  >  
  <  Body  >  
  <  Div  Class  = "Warp"  >  
  <  Canvas  ID  = "Air" > </  Canvas  >  
  </  Div  >  
  <  Script  >  
  VaR  Canvas_air  = $ (  "  # Air  "  );
Alert (canvas_air );
Alert (document. getelementbyid ("Air "));
  VaR  Air_2d  =  Canvas_air.getcontext (  "  2d "  );
  VaR  Air_img  =  New  Image ();
Air_img.src  =  "  Images/Boston-III-48px.png  " ;
Air_2d.drawimage (air_img,  0  ,  0  );
  </  Script  >  
  </  Body  >  
  </  Html > 

The Alert () values are [object] and [object htmlcanvaselement]. From here, it is not hard to see that $ ("# air") is not as expected. Let's take a look at firebug debugging,
$ ("# Air") and document. getelementbyid ("Air. The debugging result is as follows:

 
$ ("# Air") [Canvas # air]

Document. getelementbyid ("Air") Canvas # air
 

You may think of the results as well.

In fact, $ ("# air") [0] is equivalent to document. getelementbyid ("Air ")