Method eliminateUnusedStatement

lib/ConstPlugin.js:519–567

* Eliminate an unused statement. * @param {JavascriptParser} parser the parser * @param {Statement} statement the statement to remove * @param {boolean} alwaysInBlock whether to always generate curly brackets * @returns {void}

(parser, statement, alwaysInBlock)

	 * @returns {void}
	 */
	eliminateUnusedStatement(parser, statement, alwaysInBlock) {
		// Before removing the unused branch, the hoisted declarations
		// must be collected.
		//
		// Given the following code:
		//
		//     if (true) f() else g()
		//     if (false) {
		//       function f() {}
		//       const g = function g() {}
		//       if (someTest) {
		//         let a = 1
		//         var x, {y, z} = obj
		//       }
		//     } else {
		//       …
		//     }
		//
		// the generated code is:
		//
		//     if (true) f() else {}
		//     if (false) {
		//       var f, x, y, z;   (in loose mode)
		//       var x, y, z;      (in strict mode)
		//     } else {
		//       …
		//     }
		//
		// NOTE: When code runs in strict mode, `var` declarations
		// are hoisted but `function` declarations don't.
		//
		const declarations = parser.scope.isStrict
			? getHoistedDeclarations(statement, false)
			: getHoistedDeclarations(statement, true);

		const inBlock = alwaysInBlock || statement.type === "BlockStatement";

		let replacement = inBlock ? "{" : "";
		replacement +=
			declarations.length > 0 ? ` var ${declarations.join(", ")}; ` : "";
		replacement += inBlock ? "}" : "";

		const dep = new ConstDependency(
			`// removed by dead control flow\n${replacement}`,
			/** @type {Range} */ (statement.range)
		);
		dep.loc = /** @type {SourceLocation} */ (statement.loc);
		parser.state.module.addPresentationalDependency(dep);
	}
}

module.exports = ConstPlugin;