Function getHeader

example/tests/gm_xhr_test.js:1952–1956

(headersStr, key)

    if (aj !== bj) throw new Error(msg ? `${msg}: expected ${bj}, got ${aj}` : `deep equal failed`);
  }
  function getHeader(headersStr, key) {
    const lines = (headersStr || "").split(/\r?\n/);
    const line = lines.find((l) => l.toLowerCase().startsWith(key.toLowerCase() + ":"));
    return line ? line.split(":").slice(1).join(":").trim() : "";
  }
  function objectProps(o) {
    if (!o || typeof o !== "object") return "not an object";
    let z, oD, zD;