function getFileExtension(filename)
{
  var ext = /^.+\.([^.]+)$/.exec(filename);
  return ext == null ? "" : ext[1];
}

测试了

"a.b"     (=> "b") 
"a"       (=> "") 
".hidden" (=> "") 
""        (=> "") 
null      (=> "")  

也

"a.b.c.d" (=> "d")
".a.b"    (=> "b")
"a..b"    (=> "b")

function getFileExtension(filename)
{
  var ext = /^.+\.([^.]+)$/.exec(filename);
  return ext == null ? "" : ext[1];
}

测试了

"a.b"     (=> "b") 
"a"       (=> "") 
".hidden" (=> "") 
""        (=> "") 
null      (=> "")  

也

"a.b.c.d" (=> "d")
".a.b"    (=> "b")
"a..b"    (=> "b")

如果你正在处理web url，你可以使用:

function getExt(filepath){
     return filepath.split("?")[0].split("#")[0].split('.').pop();
}

getExt("../js/logic.v2.min.js") // js
getExt("http://example.net/site/page.php?id=16548") // php
getExt("http://example.net/site/page.html#welcome.to.me") // html
getExt("c:\\logs\\yesterday.log"); // log

演示:https://jsfiddle.net/squadjot/q5ard4fj/

Code

/**
 * Extract file extension from URL.
 * @param {String} url
 * @returns {String} File extension or empty string if no extension is present.
 */
var getFileExtension = function (url) {
    "use strict";
    if (url === null) {
        return "";
    }
    var index = url.lastIndexOf("/");
    if (index !== -1) {
        url = url.substring(index + 1); // Keep path without its segments
    }
    index = url.indexOf("?");
    if (index !== -1) {
        url = url.substring(0, index); // Remove query
    }
    index = url.indexOf("#");
    if (index !== -1) {
        url = url.substring(0, index); // Remove fragment
    }
    index = url.lastIndexOf(".");
    return index !== -1
        ? url.substring(index + 1) // Only keep file extension
        : ""; // No extension found
};

Test

注意，在没有查询的情况下，片段可能仍然存在。

"https://www.example.com:8080/segment1/segment2/page.html?foo=bar#fragment" --> "html"
"https://www.example.com:8080/segment1/segment2/page.html#fragment"         --> "html"
"https://www.example.com:8080/segment1/segment2/.htaccess?foo=bar#fragment" --> "htaccess"
"https://www.example.com:8080/segment1/segment2/page?foo=bar#fragment"      --> ""
"https://www.example.com:8080/segment1/segment2/?foo=bar#fragment"          --> ""
""                                                                          --> ""
null                                                                        --> ""
"a.b.c.d"                                                                   --> "d"
".a.b"                                                                      --> "b"
".a.b."                                                                     --> ""
"a...b"                                                                     --> "b"
"..."                                                                       --> ""

JSLint

0的警告。

快速和正确的路径工作

(filename.match(/[^\\\/]\.([^.\\\/]+)$/) || [null]).pop()

一些边缘情况

/path/.htaccess => null
/dir.with.dot/file => null

使用split的解决方案很慢，使用lastIndexOf的解决方案不能处理边缘情况。

我只是想分享这个。

fileName.slice(fileName.lastIndexOf('.'))

虽然这有一个缺点，即没有扩展名的文件将返回最后一个字符串。 但如果你这样做，这将解决所有问题:

   function getExtention(fileName){
     var i = fileName.lastIndexOf('.');
     if(i === -1 ) return false;
     return fileName.slice(i)
   }