closure-compiler

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Array.pop and Array.shift methods do not get type-checked correctly, at least not by Typescript standards.

Example:

/**
 * @param {Array<string>} names
 */
function hello(names) {
  /** @type {string} */
  const name = names.pop() // should raise an error, `name` can be undefined
}

/**
 * @param {Array<string>} names
 */
function hello(names) {
  /** @type {string} */
  const name = names.shift() // should raise an error, `name` can be undefined
}

Compiler Version: v20221102

Build command:

java -jar ./scripts/closureCompiler.jar \
  --entry_point=./src/js/index.js \
  --js=./src/**.js \
  --dependency_mode=PRUNE \
  --warning_level=VERBOSE \
  --js_output_file=./dist/bundle.js \
  --module_resolution=WEBPACK \
  --compilation_level=ADVANCED \
  --jscomp_error=checkDebuggerStatement \
  --jscomp_error=unusedLocalVariables \
  --jscomp_error=reportUnknownTypes \
  --jscomp_error=strictCheckTypes;

The reason for this behavior is that the standard externs definitions for these methods don't include undefined as a possible return value.

e.g.

https://github.com/google/closure-compiler/blob/a4329316423d8478452e6330c6b887dd97ddef00/externs/es3.js#L860-L869

The trouble with fixing this is that it will likely cause a large amount of existing code to start failing to compile with type errors.

However, for a new project, you could definitely use modified versions of the externs that have more accurate definitions.