Why should you care?

When keys are objects or you need guaranteed insertion order, Map beats plain {}.

See it live — copy this example

Paste into an HTML file or the browser console (F12). Use Run below when the live editor is available.

const scores = new Map();
scores.set("alice", 10);
scores.set("bob", 15);
console.log(scores.get("alice"));
console.log(scores.size);

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• set stores a pair; get reads by key.
• Any value can be a key, including numbers or objects.

Practice next

1. set and get scores for alice and bob.
2. Use an object as a key and retrieve its value.
3. Iterate with forEach((v, k) => ...).
4. Store DOM element references as keys mapping to metadata objects.
5. Convert Map entries to array with [...scores.entries()].

Remember

new Map() set/get/has/delete Keys can be any type

ScriptVerse session cache

A Map caches fetched user profiles keyed by userId object references in a long-lived SPA shell.

Outcome: Maps avoid key coercion bugs when IDs are numbers vs strings.