different-variables-types

In JavaScript, you can assign any value to any variable. But in TypeScript, a variable's type is generally fixed. Using different variables for different concepts improves type safety and code clarity.

Union types are harder to work with and obscure the code's intent.

const makes code easier for both humans and TypeScript to understand.

當想要重複使用變數時使用。當變數改變類型時使用。將聯合類型用於多種目的時使用。 來源：marius-townhouse/effective-typescript-skills。