Remove a Map entry and detect whether it existed.
TypeScript: Map.delete returns true only when an entry was present.
const values = new Map([["temporary", 1]]);
console.log(values.delete("temporary"));
console.log(values.delete("temporary"));
console.log(values.size);Expected output EXAMPLE
true false 0
Details
Requires TypeScript and Node.js. Save as snippet.ts, compile with tsc --strict --target ES2022 --module commonjs snippet.ts, then run node snippet.js. Map.delete returns true only when an entry was present.
Tested on Ubuntu 24.04.5 LTS · · TypeScript 5.9.3; Node.js v18.19.1 · bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Snippet process uid 65534 with a read-only root filesystem and temporary working files. Networking disabled. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged process) / C.UTF-8
- Interpreter invocation
tsc --strict --target ES2022 --module commonjs snippet.ts && node snippet.js- Container image ID
sha256:ec91410a8f6ec3e985830b5e3a0560306d36f8c1c5ccd91a6699abe707123fa3- Code SHA-256
665cf9d0cd1517267fde9d42c478fa6e9e1b59e8f027a0783943b949f344c9cd- Dependencies
- bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
true false 0
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.