Sample: convert from plural String#replace'es change to compact one reduce call. This script can be executed by GAS (some syntaxes require V8 engine support).

replace_sample.js

function ordinally_replace_sample() {
  const content = getContent();
  let replaced  = content;
  replaced = replaced.replace(/&/g, "&");
  replaced = replaced.replace(/</g, "&lt;");
  replaced = replaced.replace(/>/g, "&gt;");
  replaced = replaced.replace(/"/g, "&quot;");
  replaced = replaced.replace(/'/g, "&apos;");
  console.log("ordinally: " + replaced);
}

function reduce_replace_sample() {
  const content = getContent();
  const replacer = [[/&/g, "amp"], [/</g, "lt"], [/>/g, "gt"], [/"/g, "quot"], [/'/g, "apos"]];
  const replaced = replacer.reduce((acc, [re, ent]) => acc.replace(re, `&${ent};`), content);
  console.log("reduce: " + replaced);
}

function getContent() {
  return `今日は"いい天気"ですね<!>&<どこか>行きたいですね`;
}