JS：最优化的方法是从字符串中的路径中删除文件名？ [英] JS: Most optimized way to remove a filename from a path in a string?

问题描述

我的字符串格式如下：

path / to / a / filename.txt

I have strings formatted as follows:
path/to/a/filename.txt

现在我想做一些字符串操作，这使我能够非常有效地从这段代码中删除filename.txt部分。换句话说，我希望我的字符串变为：

path / to / a /

Now I'd like to do some string manipulation which allows me to very efficiently remove the "filename.txt" part from this code. In other words, I want my string to become this:
path/to/a/

最有效的方法是什么？目前我正在分割字符串并重新连接除最后一个元素之外的单独元素，但我感觉这是一种真正的，非常低效的方法。这是我当前效率低下的代码：

What's the most efficient way to do this? Currently I'm splitting the string and reconnecting the seperate elements except for the last one, but I get the feeling this is a really, REALLY inefficient way to do it. Here's my current, inefficient code:

res.getPath = function(file)
{
  var elem = file.split("/");
  var str = "";
  for (var i = 0; i < elem.length-1; i++)
    str += elem[i] + "/";
  return str;
}

推荐答案

使用lastIndexOf（）查找最后一个斜杠的位置，并使用substring（）获取斜杠之前的部分。

Use lastIndexOf() to find the position of the last slash and get the part before the slash with substring().

str.substring(0, str.lastIndexOf("/"));

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