How to use the binary.encodeUtf8 function in binary

function encodeCommit(body) {
    var str = "tree " + body.tree;
    for (var i = 0, l = body.parents.length; i < l; ++i) {
      str += "\nparent " + body.parents[i];
    }
    str += "\nauthor " + formatPerson(body.author) +
           "\ncommitter " + formatPerson(body.committer) +
           "\n\n" + body.message;
    return binary.encodeUtf8(str);
  }

function encodeBlob(blob) {
    if (typeof blob === "string") return {
      content: binary.encodeUtf8(blob),
      encoding: "utf-8"
    };
    if (binary.isBinary(blob)) return {
      content: binary.toBase64(blob),
      encoding: "base64"
    };
    throw new TypeError("Invalid blob type, must be binary of string");
  }

function encodeTag(body) {
    var str = "object " + body.object +
      "\ntype " + body.type +
      "\ntag " + body.tag +
      "\ntagger " + formatPerson(body.tagger) +
      "\n\n" + body.message;
    return binary.encodeUtf8(str);
  }