get the static part of a RegExp-CodePudding

I want to get the static part of a RegExp string, which 100% guaranteed to not have a regex-specific characters, except the grouping parentheses ().

for instance, this regex /path\/config-(. )\/.js/ has a static part /path/config- until the character '.'

use cases:

I want to search for all matched entries inside a folder that have too many files and subfolders.

so, it is a bit faster to start searching from the basic path /path that doesn't needed to be matched against, instead of starting from the root directory.

CodePudding user response：

Use regex to parse your regex. For the example you showed, you can use:

firstRegexExpr = '/path\/config-(. )\/.js/';
secondRegexExpr = /(.*)\(/;
match = firstRegexExpr.match(secondRegexExpr);

console.log(`Path: ${match[1]}`); // Path: /path/config-

CodePudding user response：

Based on the "special characters" in this answer, you can use:

const extractPrefix = (re) => {
  const partPattern = /^[^.* ?^${}()|[\]] /g;
  let part = re.source.match(partPattern)[0];
  if (part) {
    part = part.replace(/\\/g, "");
  }
  return part;
};

const re = /path\/config-(. )\/.js/g;
document.getElementById("output").textContent = extractPrefix(re);

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