javascript - 如何从 Javascript 中的文件名字符串中提取扩展名？

Question

<分区>

Answer 1

适用于以下所有输入的变体:

• "file.name.with.dots.txt"
• “文件.txt”
• "file"
• ""
• null
• 未定义

会是:

var re = /(?:\.([^.]+))?$/;

var ext = re.exec("file.name.with.dots.txt")[1];   // "txt"
var ext = re.exec("file.txt")[1];                  // "txt"
var ext = re.exec("file")[1];                      // undefined
var ext = re.exec("")[1];                          // undefined
var ext = re.exec(null)[1];                        // undefined
var ext = re.exec(undefined)[1];                   // undefined

解释

(?:         # begin non-capturing group
  \.        #   a dot
  (         #   begin capturing group (captures the actual extension)
    [^.]+   #     anything except a dot, multiple times
  )         #   end capturing group
)?          # end non-capturing group, make it optional
$           # anchor to the end of the string