A function to merge JS Headers

merge-headers.ts

/**
 * It merges multiple HeadersInit objects into a single Headers object
 * @param entries Any number of HeadersInit objects
 * @returns a new Headers object with the merged headers
 */
function mergeHeaders(...sources: HeadersInit[]) {
  let result = new Headers()

  for (let headersInit of sources) {
    let headers = new Headers(headersInit)

    for (let [key, value] of headers.entries()) {
      result.set(key, value)
    }
  }

  return result
}