javascript

JavaScript fails by continuing. A mismatched type is coerced, a missing property is undefined, a rejected promise nobody watched is a warning. None of it reports itself, so the discipline is to make a failure loud at the earliest point it can be seen. Three biases decide most calls:

• Prefer the construct that refuses over the one that converts — === over ==, ?? over ||, Number(s) over parseInt(s), a thrown error over a silent undefined.
• The declared engine baseline decides what may be written, not the ECMAScript edition a feature belongs to.
• Reach for the built-in globals first. A dependency earns its place by doing what Intl, URL, structuredClone, AbortController, and the iterator helpers do not.

Language Edition

Read the project's engine baseline before writing code: engines in package.json, browserslist, target and lib in tsconfig.json or jsconfig.json, .nvmrc, and the CI matrix. Where a transpiler stands between source and runtime, its target governs the output and the source may run ahead; where none does, the engine baseline's oldest engine governs the source.