nl_tokens: 图片预加载
pl_tokens: function loadImage ( url , callback , error ) { var img = new Image ( ) ; img . src = <mask> ; if ( img . complete ) { return callback ( img ) ; } img . onload = function ( ) { img . onload = null ; callback ( img ) ; } ; img . onerror = function ( e ) { img . onerror = null ; error ( e ) ; } ; }