in slides/webgl/asset/common/codemirror/javascript.js [388:407]
function expressionInner(type, noComma) {
if (cx.state.fatArrowAt == cx.stream.start) {
var body = noComma ? arrowBodyNoComma : arrowBody;
if (type == "(") return cont(pushcontext, pushlex(")"), commasep(pattern, ")"), poplex, expect("=>"), body, popcontext);
else if (type == "variable") return pass(pushcontext, pattern, expect("=>"), body, popcontext);
}
var maybeop = noComma ? maybeoperatorNoComma : maybeoperatorComma;
if (atomicTypes.hasOwnProperty(type)) return cont(maybeop);
if (type == "function") return cont(functiondef, maybeop);
if (type == "class") return cont(pushlex("form"), classExpression, poplex);
if (type == "keyword c" || type == "async") return cont(noComma ? maybeexpressionNoComma : maybeexpression);
if (type == "(") return cont(pushlex(")"), maybeexpression, expect(")"), poplex, maybeop);
if (type == "operator" || type == "spread") return cont(noComma ? expressionNoComma : expression);
if (type == "[") return cont(pushlex("]"), arrayLiteral, poplex, maybeop);
if (type == "{") return contCommasep(objprop, "}", null, maybeop);
if (type == "quasi") return pass(quasi, maybeop);
if (type == "new") return cont(maybeTarget(noComma));
return cont();
}