setInterval () setTimeout () requestAnimationFrame () clearInterval () clearTimeout () cancelAnimationFrame () var canvas = wx . createCanvas () var ctx = canvas . getContext ( "2d" ) ctx . fillStyle = "red" ctx . fillRect ( 0 , 0 , 100 , 100 ) ctx . clearRect ( 0 , 0 , canvas . width , canvas . height ) //清除画布 ctx . fillRect ( 0 , 20 , 100 , 100 ) ctx . clearRect ( 0 , 0 , canvas . width , canvas . height ) ctx . fillRect ( 0 , 150 , 100 , 100 ) var num = 0 var timer = setInterval ( function (){ num ++ ctx . clearRect ( 0 , 0 , canvas . width , canvas . height ) ctx . fillRect ( 0 , num ++,