Remove a Map entry and detect whether it existed.
JavaScript: 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
Save as snippet.js and run node snippet.js. Uses built-in Node.js and JavaScript APIs. Map.delete returns true only when an entry was present.
Tested on Ubuntu 24.04.5 LTS · · v18.19.1 · nodejs 18.19.1+dfsg-6ubuntu5
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. 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) / C.UTF-8
- Interpreter invocation
node snippet.js- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
665cf9d0cd1517267fde9d42c478fa6e9e1b59e8f027a0783943b949f344c9cd- Dependencies
- nodejs 18.19.1+dfsg-6ubuntu5
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.