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Private Class Members
JavaScript added support for private class members in ES2022 with the # syntax. TypeScript respects that syntax, and will give you compilation errors if you try to access private members outside of the class.
class SecretAgent {
// a private field
#id: string;
constructor(id: string) {
this.#id = id;
}
// a public method
getCodeName(): string {
const idToCodeNameMap: { [key: string]: string } = {
"007": "James Bond",
"006": "Alec Trevelyan",
// Add more mappings as needed
};
return idToCodeNameMap[this.#id] || "Unknown Agent";
}
}
const bond = new SecretAgent("007");
console.log(bond.getCodeName()); // "James Bond"
// Property '#id' is not accessible outside class 'SecretAgent' because it has a private identifier.
console.log(bond.#id);
In plain JavaScript, we'd only get the error at runtime, but with the same syntax in TypeScript, we get the error at compile time. Much better!