如何检索从特定字符串开始到最后一个字符数组的字符

Question

row1: 10016/Documents/abc.pdf

row2: 10016-10017/10017/Documents/folder1/folder2/xyz.pdf

I'm trying to retrieve all the characters starting from /Documents but without the last part (file name)

In row 1, I want to retrieve /Documents/

In row 2, I want to retrieve /Documents/folder1/folder2/

I tried

var temp1 = FullPath.split("/Documents/")[0];

var A_Fpath = temp1.split("/");

A_Fpath = A_Fpath[A_Fpath.length - 1];

Answer 1

A simple regex would do the trick:

/\/Documents.*\//
/                    start the regex
 \/                  match literally a "/" (the \ is to escape the / reserved character)
   Documents         match literally the word "Documents" (case sensitive
            .*       match 0 or more characters (any characters)
              \/     match literally a "/"
                /    end the regex
   
This works because regex will attempt to match the longest possible string
of characters that match the regex.

 const row1 = "10016/Documents/abc.pdf"; const row2 = "10016-10017/10017/Documents/folder1/folder2/xyz.pdf"; const regex = /\\/Documents.*\\//; const val1 = row1.match(regex)[0]; const val2 = row2.match(regex)[0]; console.log(val1); console.log(val2);

Here's a Regex101 link to test it out and see more info about this specific regex.

Answer 2

If javascript had a grown-up regular expression engine, one could use a positive, non-capturing lookahead group to determine when to stop.

Since javascript lacks that, the simple, clearer, and more efficient way is to not use a regular expression at all. The algorithm is simple:

• Find the [first/leftmost] /Documents in the source text, then

• Find the last/rightmost occurrence of / in the source text

• Deal with the two special cases where:

  • The source string doesn't contain /Documents at all, and
  • The rightmost / is the / in /Documents

• Failing a special case as noted above, return the desired substring extending from /Documents up to and including the last /

Like this:

function getInterestingBitsFrom(path) {
  const i   = path.indexOf('/Documents');
  const j   = path.lastIndexOf('/');
  const val = i < 0   ? undefined     // no '/Documents' in string
            : i === j ? path.slice(i) // last '/' in string is the '/' in '/Documents'             
            : path.slice(i, j+1)      // '/Documents/' or '/Documents/.../'
            ;

  return retVal;  
}

This also has the laudatory benefit of being easy to understand for someone who has to figure out what you were trying to accomplish.