Using objects as key/value storage

Objects can be considered as key/value storage, like a dictionary. If you have tabular data, you can use an object to look up values rather than a switch statement or an if/else chain. This is most useful when you know that your input data is limited to a certain range.

Here is an example of a simple reverse alphabet lookup:

const alpha = {
  1:"Z",
  2:"Y",
  3:"X",
  4:"W",
  // ...
  24:"C",
  25:"B",
  26:"A"
};

const thirdLetter = alpha[2];
const lastLetter = alpha[24];

const value = 2;
const valueLookup = alpha[value];

Here is another example where an object is used instead of a switch statement to look up value.

const phoneticLookup = (val) => {
  let result = "";

  switch(val) {
    case "alpha":
      result = "Adams";
      break;
    case "bravo":
      result = "Boston";
      break;
    case "charlie":
      result = "Chicago";
      break;
    case "delta":
      result = "Denver";
      break;
    case "echo":
      result = "Easy";
      break;
    case "foxtrot":
      result = "Frank";
  }

  return result;
}

phoneticLookup("charlie");

The above code can be converted to use an object instead.

const phoneticLookup = (val) => {
  let result = "";

  const lookup = {
    "alpha": "Adams",
    "bravo": "Boston",
    "charlie": "Chicago",
    "delta": "Denver",
    "echo": "Easy",
    "foxtrot": "Frank",
  }

  result = lookup[val];

  return result;
}

phoneticLookup("charlie");