SOURCE

const external = (filename) => {
  var filename = "emoji.png";
  var index1=filename.lastIndexOf(".");  
	var index2=filename.length;
	var postf=filename.substring(index1,index2);//后缀名
  return postf;
}
console.log(external())//.png

            
console 命令行工具 X clear

                    
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console