HTML5 Exercise (1) make the stars __html

1, understand canvas
< Canvas id = "Stars" height = "+" > </canvas > This is the canvas.
2, set the body background color
< style type = "Text/css" > body {background-color:black; } </Style > 3, initializing Canvas and context
Context as the global variable var context;      function init () {//get canvas var stars = document. getElementById ("stars"); windowwidth = window.      Innerwidth; Stars.      width = windowwidth; Get context = stars. GetContext ("2d"); }
4. Define Star objects
 //Star object var  star  =  function  () {     this. x  = -1;//Sit down Mark      this. y  = -1; Ordinate      this. Text = "*"; Text      this. Font = "Italic bold 24px serif";      this. color  =  "White"; Color     //Generate coordinates      this. GetPos = function () {         var  xx  =  windowwidth  *&n Bsp Math. Random ()  //not exceeding borders          var  yy  =  600  *   Math. Random ()  //do not exceed boundary          this. x  =  Math. Floor (XX);          this. y  =  Math. Floor (YY);     }     //produce random colors, four different brightness stars &NBSP;&Nbsp;   this. GetColor = function () {         var  _r  =  Math. Random ();          if (_r < 0.2) {               this. color  =   "#0000FF";         } else  if (_r < 0.5) {       & nbsp;      this. color  =  "White";         } else  if (_r < 0.8) {       & nbsp;      this. color  =  "#989898";         } else {               this. color  =  "#B8B8B8";         }     }     //Generate randomFontSize, maximum is 15 pixels, minimum 3 pixels      this. getfont  =  function () {         var  _r  =  Math. Ra Ndom () * 12+3;          this. font  =  "italic bold " + Math. Ceil (_r) + "Px serif";      }     //initialization      T His. init = function () {         this. getpos ();      & nbsp;   this. GetColor ();          this. GetFont ();     }     //drawing      this. Draw = function () {