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HTTP Date Format And Parse

Format Dates as IMF-fixdate for HTTP headers and parse all three legacy HTTP date formats into Date objects.

JavascriptData Fetching

Code

snippet
const DAYS = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
const MONTHS = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

function pad(value) {
  return String(value).padStart(2, "0");
}

export function formatHttpDate(date = new Date()) {
  const value = date instanceof Date ? date : new Date(date);
  if (Number.isNaN(value.getTime())) throw new RangeError("invalid date");
  return DAYS[value.getUTCDay()] + ", "
    + pad(value.getUTCDate()) + " "
    + MONTHS[value.getUTCMonth()] + " "
    + value.getUTCFullYear() + " "
    + pad(value.getUTCHours()) + ":"
    + pad(value.getUTCMinutes()) + ":"
    + pad(value.getUTCSeconds()) + " GMT";
}

export function parseHttpDate(input) {
  if (typeof input !== "string") throw new TypeError("input must be a string");
  const value = Date.parse(input);
  if (Number.isNaN(value)) throw new RangeError("invalid HTTP date");
  return new Date(value);
}

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