Calculating HMAC SHA-1 in the Browser

If you’re looking for the equivalent of hash_hmac('sha1', 'string', 'secret'); in JavaScript, then here you go:

async function hmac_sha1 (str, secret) {
  // see https://stackoverflow.com/a/47332317/1134119
  let enc = new TextEncoder("utf-8");
  let key = await window.crypto.subtle.importKey(
    "raw", // raw format of the key - should be Uint8Array
    enc.encode(secret),
    { // algorithm details
      name: "HMAC",
      hash: {name: "SHA-1"}
    },
    false, // export = false
    ["sign", "verify"] // what this key can do
  );
  let signature = await window.crypto.subtle.sign(
    "HMAC",
    key,
    enc.encode(str)
  );
  let b = new Uint8Array(signature);
  return Array.prototype.map.call(b, x => x.toString(16).padStart(2, '0')).join("");
}