DOM - NATO spell selection.js

let selection;
const h = {
  0: "Zero",
  1: "One",
  2: "Two",
  3: "Three",
  4: "Four",
  5: "Five",
  6: "Six",
  7: "Seven",
  8: "Eight",
  9: "Nine",
  A: "Alpha",
  B: "Bravo",
  C: "Charlie",
  D: "Delta",
  E: "Echo",
  F: "Foxtrot",
  G: "Golf",
  H: "Hotel",
  I: "India",
  J: "Juliett",
  K: "Kilo",
  L: "Lima",
  M: "Mike",
  N: "November",
  O: "Oscar",
  P: "Papa",
  Q: "Quebec",
  R: "Romeo",
  S: "Sierra",
  T: "Tango",
  U: "Uniform",
  V: "Victor",
  W: "Whiskey",
  X: "X-ray",
  Y: "Yankee",
  Z: "Zulu",
};
if (window.getSelection) {
  selection = window.getSelection().toString();
} else if (document.selection && document.selection.type !== "Control") {
  selection = document.selection.createRange().text;
}
if (selection === undefined || selection.length === 0) {
  window.alert("Select the desired text.");
} else {
  selection = selection.trim();
  let result = "";
  let i, c, d, t;
  for (i = 0; i < selection.length; i += 1) {
    c = selection.charAt(i);
    d = encodeURIComponent(c);
    if (d === c) {
      d = h[c];
    }
    if (d === undefined) {
      t = h[c.toUpperCase()];
      if (t === undefined) {
        d = `%${c.codePointAt(0).toString(16).toUpperCase()}`;
      } else {
        d = t.toLowerCase();
      }
    }
    result += `${d} `;
  }
  window.alert(result);
}