img的绝对路径转为相对路径

$('#add_img').on('change', function(){

var objUrl = getObjectURL(this.files[0]) ;
if (objUrl) {
$(this).prev("img").attr("src", objUrl);
}

});

function getObjectURL(file) {
var url = null;
if (window.createObjectURL != undefined) { // basic
url = window.createObjectURL(file);
} else if (window.URL != undefined) { // mozilla(firefox)
url = window.URL.createObjectURL(file);
} else if (window.webkitURL != undefined) { // webkit or chrome
url = window.webkitURL.createObjectURL(file);
}
return url;
}