packages/babel-plugin-transform-new-target/src/index.js
import { declare } from "@babel/helper-plugin-utils";
import { types as t } from "@babel/core";
export default declare(api => {
api.assertVersion(7);
return {
name: "transform-new-target",
visitor: {
MetaProperty(path) {
const meta = path.get("meta");
const property = path.get("property");
const { scope } = path;
if (
meta.isIdentifier({ name: "new" }) &&
property.isIdentifier({ name: "target" })
) {
const func = path.findParent(path => {
if (path.isClass()) return true;
if (path.isFunction() && !path.isArrowFunctionExpression()) {
if (path.isClassMethod({ kind: "constructor" })) {
return false;
}
return true;
}
return false;
});
if (!func) {
throw path.buildCodeFrameError(
"new.target must be under a (non-arrow) function or a class.",
);
}
const { node } = func;
if (!node.id) {
if (func.isMethod()) {
path.replaceWith(scope.buildUndefinedNode());
return;
}
node.id = scope.generateUidIdentifier("target");
}
const constructor = t.memberExpression(
t.thisExpression(),
t.identifier("constructor"),
);
if (func.isClass()) {
path.replaceWith(constructor);
return;
}
path.replaceWith(
t.conditionalExpression(
t.binaryExpression(
"instanceof",
t.thisExpression(),
t.cloneNode(node.id),
),
constructor,
scope.buildUndefinedNode(),
),
);
}
},
},
};
});