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Types · easy

2. Basic types

number, string, boolean, and the any escape hatch.

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The primitive types mirror JavaScript's runtime primitives: `number` for all numeric values (there's no separate int/float), `string`, `boolean`, `null`, and `undefined`.

Annotations follow a colon after the identifier. TypeScript can often infer them, so annotate when it improves clarity or when there's no initializer to infer from.

ts
let blockNumber: number = 18_000_000;
let network: string = "mainnet";
let isTestnet: boolean = false;
let owner: string | undefined;

`any` disables type checking for a value entirely — useful for gradual migration, but it defeats the purpose of TypeScript if overused. Prefer `unknown` when you must accept an untyped value but still want safety.

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Check your understanding

  1. 1. How many numeric types does TypeScript have for ordinary numbers?

  2. 2. What does annotating a variable with `any` do?

  3. 3. Which type is generally safer than `any` for unknown values?

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