Node js get file extension

Question

Im creating a file upload function in node js with express 3   I would like to grab the file extension of the image  so i can rename the file and then append the file extension to it   app post   upload   function req  res  next        var is   fs createReadStream req files upload path           fileExt          I want to get the extension of the image here         os   fs createWriteStream  public images users     req session adress         fileExt         How can i get the extension of the image in node js

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Update  Since the original answer  extname   has been added to the path module  see Snowfish answer  Original answer    I m using this function to get a file extension  because I didn t find a way to do it in an easier way  but I think there is     function getExtension filename        var ext   path extname filename      split           return ext ext length - 1       you must require  path  to use it   another method which does not use the path module    function getExtension filename        var i   filename lastIndexOf           return  i  lt  0         filename substr i

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Try this one  const path   require  path     function getExt str      const basename   path basename str     const firstDot   basename indexOf         const lastDot   basename lastIndexOf         const extname   path extname basename  replace      a-z0-9      i    1       if  firstDot     lastDot        return extname         return basename slice firstDot  lastDot    extname        all are   gz  console log getExt   home charlike bar file gz     console log getExt   home charlike bar file gz      console log getExt   home charlike bar file gz cdf2     console log getExt   home charlike bar file gz quz zaz         all are   tar gz  console log getExt   home charlike bar file tar gz     console log getExt   home charlike bar file tar gz      console log getExt   home charlike bar file tar gz cdf2     console log getExt   home charlike bar file tar gz quz zaz

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path extname will do the trick in most cases  However  it will include everything after the last    including the query string and hash fragment of an http request   var path   require  path   var extname   path extname  index html username asdf      extname contains   html username asdf    In such instances  you ll want to try something like this   var regex           g     regex of illegal extension characters var extname   path extname  index html username asdf    var endOfExt   extname search regex   if  endOfExt  gt  -1        extname   extname substring 0  endOfExt        extname contains   html    Note that extensions with multiple periods  such as  tar gz   will not work at all with path extname

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A simple solution without need for require which solves the multiple period extension problem   var filename    file with long extension   var ext   filename substring filename indexOf           ext     with long extension    Or if you don t want the leading dot   var filename    file with long extension   var ext   filename substring filename indexOf      1      ext    with long extension    Make sure to test that the file has an extension too

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I believe you can do the following to get the extension of a file name   var path   require  path    path extname  index html      returns   html

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It s a lot more efficient to use the substr   method instead of split    amp  pop    Have a look at the performance differences here  http   jsperf com remove-first-character-from-string     returns   html  var path   require  path    path extname  index html   substr 1       Update August 2019 As pointed out by  xentek in the comments  substr   is now considered a legacy function  MDN documentation   You can use substring   instead  The difference between substr   and substring   is that the second argument of substr   is the maximum length to return while the second argument of substring   is the index to stop at  without including that character   Also  substr   accepts negative start positions to be used as an offset from the end of the string while substring   does not

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This solution supports querystrings   var Url   require  url    var Path   require  path     var url    http   i imgur com Mvv4bx8 jpg querystring true   var result   Path extname Url parse url  pathname        jpg

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You can use path parse path   for example  const path   require  path    const   ext     path parse   home user dir file txt

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import extname in order to return the extension the file   import   extname   from  path   extname file originalname     where file is the file  name  of form

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The following function splits the string and returns the name and extension no matter how many dots there are in the extension  It returns an empty string for the extension if there is none  Names that start with dots and or white space work also   function basext name      name   name trim     const match   name match             let prefix        if  match        prefix   match 0      name   name replace prefix            const index   name indexOf        const ext   name substring index   1    const base   name substring 0  index     ext   return  prefix   base  base     ext        ext     const  base  ext    basext  hello txt

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you can send full url here function getExtension filename        return filename split      pop        If you are using express please add the following line when configuring middleware  bodyParser   app use express bodyParser   keepExtensions  true

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var fileName   req files upload name   var arr   fileName split        var extension   arr length-1

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I do think mapping the Content-Type header in the request will also work  This will work even for cases when you upload a file with no extension   when filename does not have an extension in the request   Assume you are sending your data using HTTP POST   POST  upload2 HTTP 1 1 Host  localhost 7098 Connection  keep-alive Content-Length  1047799 Accept      Origin  http   localhost 63342 User-Agent  Mozilla 5 0  X11  Linux x86 64  AppleWebKit 537 36  KHTML     like Gecko  Chrome 51 0 2704 106 Safari 537 36 Content-Type  multipart form-data  boundary ----   WebKitFormBoundaryPDULZN8DYK3VppPp Referer  http   localhost 63342 Admin index html   ijt 3a6a054pasorvrljf8t8ea0j4h Accept-Encoding  gzip  deflate Accept-Language  en-US en q 0 8 az q 0 6 tr q 0 4 Request Payload ------WebKitFormBoundaryPDULZN8DYK3VppPp Content-Disposition  form-data  name  image   filename  blob  Content-Type  image png   ------WebKitFormBoundaryPDULZN8DYK3VppPp--   Here name Content-Type header contains the mime type of the data   Mapping this mime type to an extension will get you the file extension      Restify BodyParser converts this header in to a property with name type  File     domain      Domain        domain  null        events                  eventsCount  1        maxListeners  undefined       members                events         eventsCount  0     maxListeners  undefined    size  1047621    path    tmp upload 2a4ac9ef22f7156180d369162ef08cb8     name   blob       type   image png       hash  null    lastModifiedDate  Wed Jul 20 2016 16 12 21 GMT 0300  EEST      writeStream     WriteStream                  writable  true       domain        Domain                              events             eventsCount  0        maxListeners  undefined       path    tmp upload 2a4ac9ef22f7156180d369162ef08cb8        fd  null       flags   w        mode  438       start  undefined       pos  undefined       bytesWritten  1047621       closed  true        You can use this header and do the extension mapping  substring etc      manually  but there are also ready made libraries for this  Below two were the top results when i did a google search   mime mime-types   and their usage is simple as well    app post   upload2   function  req  res      console log mime extension req files image type         above snippet will print png to console

[javascript] Node.js get file extension

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