JavaScript Built-in Method Cheat Sheet

Ever find yourself in the middle of a LeetCode problem or debugging session and think, "Wait... what methods does Map have again?" 😅
Fear not — here's your ultimate dynamic cheat sheet to inspect and remember all the built-in methods of JavaScript objects!

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🔍 Inspect Methods Dynamically

Use this line to log all methods on a type:

console.log(Object.getOwnPropertyNames(Type.prototype));

Replace Type with Array, Map, Set, etc.

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🧱 1. Array

console.log(Object.getOwnPropertyNames(Array.prototype));

[
  "length", "constructor", "at", "concat", "copyWithin", "fill",
  "find", "findIndex", "flat", "flatMap", "includes", "indexOf",
  "join", "lastIndexOf", "pop", "push", "reverse", "shift",
  "unshift", "slice", "sort", "splice", "toLocaleString",
  "toString", "values", "keys", "entries", "forEach", "filter",
  "map", "every", "some", "reduce", "reduceRight"
]

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🔤 2. String

console.log(Object.getOwnPropertyNames(String.prototype));

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🧰 3. Object

console.log(Object.getOwnPropertyNames(Object.prototype));

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🗺️ 4. Map

console.log(Object.getOwnPropertyNames(Map.prototype));

["constructor", "clear", "delete", "get", "has", "set", "entries", "forEach", "keys", "values", "size"]

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📦 5. Set

console.log(Object.getOwnPropertyNames(Set.prototype));

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📆 6. Date

console.log(Object.getOwnPropertyNames(Date.prototype));

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🔢 7. Number

console.log(Object.getOwnPropertyNames(Number.prototype));

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🎯 8. Function

console.log(Object.getOwnPropertyNames(Function.prototype));

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🧮 9. Math (not a prototype — but still useful)

console.log(Object.getOwnPropertyNames(Math));

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🧬 10. JSON (also not a prototype)

console.log(Object.getOwnPropertyNames(JSON));

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✅ Bonus: Create Your Own Inspector

function inspect(obj) {
  return Object.getOwnPropertyNames(Object.getPrototypeOf(obj));
}

console.log(inspect([]));      // For Array
console.log(inspect("hello")); // For String
console.log(inspect(new Map()));

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🧠 Pro Tip

Many of these include non-enumerable methods, which is great for full discovery. If you want to get only enumerable keys:

console.log(Object.keys(Array.prototype));

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Now you’ve got your very own in-browser API reference — use it like a debugger’s flashlight 🔦. Happy coding!