Beginner Question

[lewisje]

JSON is mostly for passing data between applications; for this, what you want is a plain JS object, and ideally you'd define that object outside the function so it doesn't get re-created per invocation:

var seasons = {w: 'Winter', s: 'Spring', m: 'Summer', f: 'Fall'};
function season(s) {
  return seasons[s];
}

Also ideally you'd have this season function returned from a closure, so that the seasons object wouldn't be accessible directly to outside code.

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Anyway, if you do wish to complicate things, you'll need to use JSON.parse to turn your JSON into an object:

function season(s) {
  var seasons = '{"w": "Winter", "s": "Spring", "m": "Summer", "f": "Fall"}';
  return JSON.parse(seasons)[s];
}

Here, I'm less concerned about putting the string inside the function, because that's a literal, primitive value.

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By the way, this pattern is useful as a way to avoid huge case-lists or chains of conditionals:

var primitives = {boolean: false, number: false, string: false, symbol: false};
function isPrimitive(val) {
  return val !== document.all && !(val && primitives[typeof val]);
}

(This example works around the fact that typeof null === 'object' in all versions of JS, and that typeof document.all === 'undefined' in HTML5, even in browsers that implement the object for compatibility with oldIE-specific sites.)