Method setHeader

lib.commonjs/utils/fetch.js:262–264

* Set the header for %%key%% to %%value%%. All values are coerced * to a string.

(key, value)

     *  to a string.
     */
    setHeader(key, value) {
        this.#headers[String(key).toLowerCase()] = String(value);
    }
    /**
     *  Clear all headers, resetting all intrinsic headers.
     */