in lib/index.ts [373:380]
function parseFunctionBody(fn: any): ts.FunctionExpression {
const setup = `const myFn = ${stringifyFunction(fn)};`;
const srcFile = ts.createSourceFile('test.ts', setup, ts.ScriptTarget.Latest, true);
const statement = srcFile.statements[0] as ts.VariableStatement;
const decl = statement.declarationList.declarations[0];
const init = decl.initializer as ts.FunctionExpression;
return init;
}