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index.ts
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index.ts
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import {
assignmentExpression,
expressionStatement,
identifier,
} from "@babel/types";
import type * as t from "@babel/types";
import type { NodePath, Visitor } from "@babel/traverse";
export type EmitFunction = (
id: t.Identifier,
idName: string,
hasInit: boolean,
) => any;
type State = {
kind: "var" | "let";
emit: EmitFunction;
};
type Unpacked<T> = T extends (infer U)[] ? U : T;
const visitor: Visitor<State> = {
Scope(path, state) {
if (state.kind === "let") path.skip();
},
FunctionParent(path) {
path.skip();
},
VariableDeclaration(path, state) {
if (state.kind && path.node.kind !== state.kind) return;
const nodes = [];
const declarations: ReadonlyArray<
NodePath<Unpacked<t.VariableDeclaration["declarations"]>>
> = path.get("declarations");
let firstId;
for (const declar of declarations) {
firstId = declar.node.id;
if (declar.node.init) {
nodes.push(
expressionStatement(
assignmentExpression("=", declar.node.id, declar.node.init),
),
);
}
for (const name of Object.keys(declar.getBindingIdentifiers())) {
state.emit(identifier(name), name, declar.node.init !== null);
}
}
// for (var i in test)
if (path.parentPath.isFor({ left: path.node })) {
path.replaceWith(firstId);
} else {
path.replaceWithMultiple(nodes);
}
},
};
export default function hoistVariables(
path: NodePath,
emit: EmitFunction,
kind: "var" | "let" = "var",
) {
path.traverse(visitor, { kind, emit });
}