/
index.js
51 lines (46 loc) 路 1.55 KB
/
index.js
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import { declare } from "@babel/helper-plugin-utils";
import syntaxNullishCoalescingOperator from "@babel/plugin-syntax-nullish-coalescing-operator";
import { types as t } from "@babel/core";
export default declare((api, { loose = false }) => {
api.assertVersion(7);
return {
name: "proposal-nullish-coalescing-operator",
inherits: syntaxNullishCoalescingOperator,
visitor: {
LogicalExpression(path) {
const { node, scope } = path;
if (node.operator !== "??") {
return;
}
let ref = scope.maybeGenerateMemoised(node.left);
let assignment;
// skip creating extra reference when `left` is static
if (ref === null) {
ref = node.left;
assignment = t.cloneNode(node.left);
} else {
assignment = t.assignmentExpression("=", ref, node.left);
}
path.replaceWith(
t.conditionalExpression(
// We cannot use `!= null` in spec mode because
// `document.all == null` and `document.all` is not "nullish".
loose
? t.binaryExpression("!=", assignment, t.nullLiteral())
: t.logicalExpression(
"&&",
t.binaryExpression("!==", assignment, t.nullLiteral()),
t.binaryExpression(
"!==",
t.cloneNode(ref),
scope.buildUndefinedNode(),
),
),
t.cloneNode(ref),
node.right,
),
);
},
},
};
});