JavaScript Navigator deprecatedReplaceInURN() Method

const lines = [
  "deprecatedReplaceInURN: " +
    (typeof navigator.deprecatedReplaceInURN === "function"
      ? "available"
      : "missing"),
  "isSecureContext: " + window.isSecureContext
];
console.log(lines.join("\n"));

function isAllowedReplacementKey(key) {
  return /^\$\{.+\}$/.test(key) || /^%%.+%%$/.test(key);
}

const samples = ["${foo}", "%%baz%%", "foo", "{bar}"];
console.log(
  samples
    .map((k) => k + ": " + (isAllowedReplacementKey(k) ? "allowed" : "invalid"))
    .join("\n")
);

async function tryMdnStyleReplace(exampleURN) {
  if (typeof navigator.deprecatedReplaceInURN !== "function") {
    return "API missing — cannot substitute fenced URN URLs here";
  }
  if (!exampleURN) {
    return "No URN / FencedFrameConfig — obtain one from an auction API first";
  }
  await navigator.deprecatedReplaceInURN(exampleURN, {
    "${foo}": "1",
    "${bar}": "2",
    "%%baz%%": "3"
  });
  return "Substitution requested (internal URL updated by the browser)";
}

tryMdnStyleReplace(null).then(console.log);

async function replaceWithGuardedKeys(urn, replacements) {
  if (typeof navigator.deprecatedReplaceInURN !== "function") {
    return "API missing";
  }
  const bad = Object.keys(replacements).filter(
    (k) => !(/^\$\{.+\}$/.test(k) || /^%%.+%%$/.test(k))
  );
  if (bad.length) {
    return "Blocked invalid keys: " + bad.join(", ");
  }
  try {
    await navigator.deprecatedReplaceInURN(urn, replacements);
    return "OK";
  } catch (err) {
    return "Error: " + err.name;
  }
}

replaceWithGuardedKeys("urn:example", { foo: "1", "${bar}": "2" }).then(console.log);

function shouldUseDeprecatedReplaceInURN(options) {
  if (!options || !options.migratingFencedFrameCreatives) {
    return "Skip — not migrating fenced-frame ad creatives";
  }
  if (typeof navigator.deprecatedReplaceInURN !== "function") {
    return "Skip — API unavailable in this browser";
  }
  return "Legacy only — prefer not to adopt; API is deprecated";
}

console.log(shouldUseDeprecatedReplaceInURN({ migratingFencedFrameCreatives: false }));
console.log(shouldUseDeprecatedReplaceInURN({ migratingFencedFrameCreatives: true }));