javascript 获取文件扩展名

var filename = 'najasm.ssds.zip'.split('');
var extName = '';
for(var i = filename.length-1; i>0; i--){
	if(~'.'.indexOf(filename[i])){
		break;
	}else{
		extName+=filename[i]
	}
	
}
var fileExtName = extName.split("").reverse().join("");
console.log(fileExtName);



	正则表达式

var fileName = 'asda.asdas.asdasda.zip';

var fileExt = fileName.replace(/.+\./, "").toLowerCase();
console.log(fileExt);