使用JavaScript实现node.js中的path.join方法


            Node.JS中的 path.join 非常方便，能直接按相对或绝对合并路径，使用： path.join([path1], [path2], [...])，有时侯前端也需要这种方法，如何实现呢？



其实直接从 node.js 的 path.js 拿到源码加工一下就可以了：

1. 将 const 等 es6 属性改为 var，以便前端浏览器兼容

2. 添加一个判断路戏分隔符的变量 sep，即左斜杠还是右斜杠，以第一个路戏分隔符为准

3. 将引用的变量和函数放到一个文件里就可以了：

Path 的源码： http://github.com/nodejs/node/blob/master/lib/path.js







var CHAR_FORWARD_SLASH = 47

var CHAR_BACKWARD_SLASH = 92

var CHAR_DOT = 46

function isPathSeparator(code) {

 return code === CHAR_FORWARD_SLASH || code === CHAR_BACKWARD_SLASH;

}

function isPosixPathSeparator(code) {

 return code === CHAR_FORWARD_SLASH;

}

function normalize(path) {

 if (path.length === 0)

  return '.';

 var isAbsolute = path.charCodeAt(0) === CHAR_FORWARD_SLASH;

 var trailingSeparator =

  path.charCodeAt(path.length - 1) === CHAR_FORWARD_SLASH;

 // Normalize the path

 path = normalizeString(path, !isAbsolute, '/', isPosixPathSeparator);

 if (path.length === 0 && !isAbsolute)

  path = '.';

 if (path.length > 0 && trailingSeparator)

  path += '/';

 if (isAbsolute)

  return '/' + path;

 return path;

}

function normalizeString(path, allowAboveRoot, separator, isPathSeparator) {

 var res = '';

 var lastSegmentLength = 0;

 var lastSlash = -1;

 var dots = 0;

 var code;

 for (var i = 0; i <= path.length; ++i) {

  if (i < path.length)

   code = path.charCodeAt(i);

  else if (isPathSeparator(code))

   break;

  else

   code = CHAR_FORWARD_SLASH;

  if (isPathSeparator(code)) {

   if (lastSlash === i - 1 || dots === 1) {

    // NOOP

   } else if (lastSlash !== i - 1 && dots === 2) {

    if (res.length < 2 || lastSegmentLength !== 2 ||

      res.charCodeAt(res.length - 1) !== CHAR_DOT ||

      res.charCodeAt(res.length - 2) !== CHAR_DOT) {

     if (res.length > 2) {

      const lastSlashIndex = res.lastIndexOf(separator);

      if (lastSlashIndex !== res.length - 1) {

       if (lastSlashIndex === -1) {

        res = '';

        lastSegmentLength = 0;

       } else {

        res = res.slice(0, lastSlashIndex);

        lastSegmentLength = res.length - 1 - res.lastIndexOf(separator);

       }

       lastSlash = i;

       dots = 0;

       continue;

      }

     } else if (res.length === 2 || res.length === 1) {

      res = '';

      lastSegmentLength = 0;

      lastSlash = i;

      dots = 0;

      continue;

     }

    }

    if (allowAboveRoot) {

     if (res.length > 0)

      res += `${separator}..`;

     else

      res = '..';

     lastSegmentLength = 2;

    }

   } else {

    if (res.length > 0)

     res += separator + path.slice(lastSlash + 1, i);

    else

     res = path.slice(lastSlash + 1, i);

    lastSegmentLength = i - lastSlash - 1;

   }

   lastSlash = i;

   dots = 0;

  } else if (code === CHAR_DOT && dots !== -1) {

   ++dots;

  } else {

   dots = -1;

  }

 }

 return res;

}

function join() {

 if (arguments.length === 0)

  return '.';

 var sep = arguments[0].indexOf('/') > -1 ? '/' : '\\'

 var joined;

 var firstPart;

 for (var i = 0; i < arguments.length; ++i) {

  var arg = arguments[i];

  if (arg.length > 0) {

   if (joined === undefined)

    joined = firstPart = arg;

   else

    joined += sep + arg;

  }

 }

 if (joined === undefined)

  return '.';

 var needsReplace = true;

 var slashCount = 0;

 if (isPathSeparator(firstPart.charCodeAt(0))) {

  ++slashCount;

  var firstLen = firstPart.length;

  if (firstLen > 1) {

   if (isPathSeparator(firstPart.charCodeAt(1))) {

    ++slashCount;

    if (firstLen > 2) {

     if (isPathSeparator(firstPart.charCodeAt(2)))

      ++slashCount;

     else {

      // We matched a UNC path in the first part

      needsReplace = false;

     }

    }

   }

  }

 }

 if (needsReplace) {

  // Find any more consecutive slashes we need to replace

  for (; slashCount < joined.length; ++slashCount) {

   if (!isPathSeparator(joined.charCodeAt(slashCount)))

    break;

  }

  // Replace the slashes if needed

  if (slashCount >= 2)

   joined = sep + joined.slice(slashCount);

 }

 return normalize(joined);

}



使用：





join('../var/www', '../abc')

> "../var/abc"

join('../var/www', '\abc')

../var/www/abc



总结



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