因此，警報會給出寬度和高度的不確定值。我認為img.onload計算中圖像的w和h值未傳遞給要返回的值，或者可能在onload計算它們之前返回了w和h ：function getMeta(url){ var w; var h; var img=new Image; img.src=url; img.onload=function(){w=this.width; h=this.height;}; return {w:w,h:h}    }// "http://snook.ca/files/mootools_83_snookca.png" //1024x678// "http://shijitht.files.wordpress.com/2010/08/github.png" //128x128var end = getMeta("http://shijitht.files.wordpress.com/2010/08/github.png");var w = end.w;var h = end.h;alert(w+'width'+h+'height');如何讓警報顯示正確的寬度和高度？http://jsfiddle.net/YtqXk/