const path = require("path");
const os = require("os");

console.log("/foo/bar/file.txt", "=>", getAbsolutePath("/foo/bar/file.txt"));
console.log("foo/bar/file.txt", "=>", getAbsolutePath("foo/bar/file.txt"));
console.log("../../foo/bar/file.txt", "=>", getAbsolutePath("../../foo/bar/file.txt"));
console.log("~/file.txt", "=>", getAbsolutePath("~/file.txt"));
console.log("/~/file.txt", "=>", getAbsolutePath("/~/file.txt"));
console.log("/../../file.txt", "=>", getAbsolutePath("/../../file.txt"));

function getAbsolutePath(filepath, delim = "/") {
  // Dependencies:
  // const path = require("path");
  // const os = require("os");
  if (filepath == null || typeof filepath !== "string") throw Error("invalid filepath");
  const homedir = os.homedir();
  filepath = filepath.replace(/\~/g, homedir + delim);
  return path.resolve(filepath);
}

/* output:
/foo/bar/file.txt => /foo/bar/file.txt
foo/bar/file.txt => /home/<user>/xxx/yyy/foo/bar/file.txt
../../foo/bar/file.txt => /home/<user>/foo/bar/file.txt
~/file.txt => /home/<user>/file.txt
/~/file.txt => /home/<user>/file.txt
/../../file.txt => /file.txt
*/