Merge pull request #250 from SarahIsWeird/main

Fail script processing when reassignment to const variable is detected

Author: samualtnorman

src/processScript/index.ts

@@ -444,4 +444,9 @@ if (import.meta.vitest) {
 			(0, eval)(`(${script})`)(import.meta.vitest)
 		})
 	}
+
+	const reassignmentTestSource = `export default () => { const i = 0; i = 1; }`
+	expect(async (): Promise<any> => await processScript(reassignmentTestSource, { scriptName: true, minify: false }))
+		.rejects
+		.toThrowError(`Reassignment to const variable i is not allowed!`)
 }

src/processScript/transform.ts

@@ -881,8 +881,22 @@ export function transform(
 				parent.superClass = t.identifier(`Object`)
 		},
 		VariableDeclaration({ node: variableDeclaration }) {
-			if (variableDeclaration.kind == `const`)
+			if (variableDeclaration.kind == `const`) {
 				variableDeclaration.kind = `let`
+				variableDeclaration.extra = {
+					...variableDeclaration.extra,
+					usedToBeConst: true,
+				}
+			}
+		},
+		AssignmentExpression({ node: assignment, scope }) {
+			const lhs = assignment.left
+			if (lhs.type != `Identifier`) return
+
+			const binding = scope.getBinding(lhs.name)
+			if (binding?.path?.parentPath?.node?.extra?.usedToBeConst) {
+				throw new Error(`Reassignment to const variable ${lhs.name} is not allowed!`);
+			}
 		},
 		ThisExpression: path => {
 			path.replaceWith(t.identifier(`undefined`))