forked from babel/babel
/
buildOptimizedSequenceExpression.js
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/
buildOptimizedSequenceExpression.js
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import { types as t } from "@babel/core";
// tries to optimize sequence expressions in the format
// (a = b, ((c) => d + e)(a))
// to
// (a = b, a + e)
const buildOptimizedSequenceExpression = ({ assign, call, path }) => {
const { left: placeholderNode, right: pipelineLeft } = assign;
const { callee: calledExpression } = call;
let optimizeArrow =
t.isArrowFunctionExpression(calledExpression) &&
t.isExpression(calledExpression.body) &&
!calledExpression.async &&
!calledExpression.generator;
let param;
if (optimizeArrow) {
const { params } = calledExpression;
if (params.length === 1 && t.isIdentifier(params[0])) {
param = params[0];
} else if (params.length > 0) {
optimizeArrow = false;
}
} else if (t.isIdentifier(calledExpression, { name: "eval" })) {
const evalSequence = t.sequenceExpression([
t.numericLiteral(0),
calledExpression,
]);
call.callee = evalSequence;
path.scope.push({ id: placeholderNode });
return t.sequenceExpression([assign, call]);
}
if (optimizeArrow && !param) {
// Arrow function with 0 arguments
return t.sequenceExpression([pipelineLeft, calledExpression.body]);
}
path.scope.push({ id: placeholderNode });
if (param) {
path.get("right").scope.rename(param.name, placeholderNode.name);
return t.sequenceExpression([assign, calledExpression.body]);
}
return t.sequenceExpression([assign, call]);
};
export default buildOptimizedSequenceExpression;