How to pass a very long string to the background server? (in the case of vue's axios+nodejs+express) - Codes Helper

I now need to pass a string of special length to the background server, as shown in figure

{"c":1549473758948,"e":253402300799000,"v":"[{\"id\":1,\"fileName\":\"2016_Book_PsychometricFrameworkForModeli\",\"cover\":\"http://192.168.1.102:5070/img/Education/2016_Book_PsychometricFrameworkForModeli.jpeg\",\"title\":\"Psychometric Framework for Modeling Parental Involvement and Reading Literacy\",\"author\":\"Annemiek Punter, Cees A. W. Glas and Martina R. M. Meelissen\",\"publisher\":\"Springer International Publishing, Cham\",\"bookId\":\"2016_Book_PsychometricFrameworkForModeli\",\"category\":4,\"categoryText\":\"Education\",\"language\":\"en\",\"rootFile\":\"OEBPS/content.opf\",\"selected\":false,\"cache\":false,\"haveRead\":0,\"type\":1},{\"type\":4,\"cache\":true,\"selected\":false,\"fileName\":\"2013_Book_ManagingRiskAndInformationSecu\",\"title\":\"2013_Book_ManagingRiskAndInformationSecu\",\"id\":2},{\"id\":3,\"fileName\":\"2016_Book_SecondaryAnalysisOfElectronicH\",\"cover\":\"http://192.168.1.102:5070/img/MedicineAndPublicHealth/2016_Book_SecondaryAnalysisOfElectronicH.jpeg\",\"title\":\"Secondary Analysis of Electronic Health Records\",\"author\":\"MIT Critical Data\",\"publisher\":\"Springer International Publishing, Cham\",\"bookId\":\"2016_Book_SecondaryAnalysisOfElectronicH\",\"category\":17,\"categoryText\":\"MedicineAndPublicHealth\",\"language\":\"en\",\"rootFile\":\"OEBPS/content.opf\",\"selected\":false,\"cache\":false,\"haveRead\":0,\"type\":1},{\"type\":4,\"cache\":true,\"selected\":false,\"fileName\":\"2017_Book_IntelligentHumanComputerIntera\",\"title\":\"2017_Book_IntelligentHumanComputerIntera\",\"id\":4},{\"type\":4,\"cache\":true,\"selected\":false,\"fileName\":\"2018_Book_TheHuaweiAndSnowdenQuestions\",\"title\":\"2018_Book_TheHuaweiAndSnowdenQuestions\",\"id\":5},{\"id\":6,\"itemList\":[{\"id\":1,\"fileName\":\"2018_Book_DiseasesOfTheAbdomenAndPelvis2\",\"cover\":\"http://192.168.1.102:5070/img/MedicineAndPublicHealth/978-3-319-75019-4_CoverFigure.jpg\",\"title\":\"Diseases of the Abdomen and Pelvis 20182021\",\"author\":\"Juerg Hodler\",\"publisher\":\"Springer International Publishing\",\"bookId\":\"2018_Book_DiseasesOfTheAbdomenAndPelvis2\",\"category\":17,\"categoryText\":\"MedicineAndPublicHealth\",\"language\":\"en\",\"rootFile\":\"OEBPS/package.opf\",\"selected\":true,\"cache\":false,\"haveRead\":0,\"type\":1},{\"id\":2,\"fileName\":\"2016_Book_AHistoryOfRadionuclideStudiesI\",\"cover\":\"http://192.168.1.102:5070/img/MedicineAndPublicHealth/978-3-319-28624-2_CoverFigure.jpg\",\"title\":\"A History of Radionuclide Studies in the UK\",\"author\":\"Ralph McCready\",\"publisher\":\"Springer International Publishing\",\"bookId\":\"2016_Book_AHistoryOfRadionuclideStudiesI\",\"category\":17,\"categoryText\":\"MedicineAndPublicHealth\",\"language\":\"en\",\"rootFile\":\"OEBPS/package.opf\",\"selected\":true,\"cache\":false,\"haveRead\":0,\"type\":1},{\"id\":3,\"fileName\":\"2016_Book_PublicHealthEthicsCasesSpannin\",\"cover\":\"http://192.168.1.102:5070/img/MedicineAndPublicHealth/2016_Book_PublicHealthEthicsCasesSpannin.jpeg\",\"title\":\"Public Health Ethics: Cases Spanning the Globe\",\"author\":\"Drue H. Barrett, Leonard W. Ortmann, Angus Dawson, Carla Saenz, Andreas Reis and Gail Bolan\",\"publisher\":\"Springer International Publishing, Cham\",\"bookId\":\"2016_Book_PublicHealthEthicsCasesSpannin\",\"category\":17,\"categoryText\":\"MedicineAndPublicHealth\",\"language\":\"en\",\"rootFile\":\"OEBPS/content.opf\",\"selected\":true,\"cache\":false,\"haveRead\":0,\"type\":1}],\"selected\":false,\"title\":\"test\",\"type\":2},{\"id\":7,\"fileName\":\"2018_Book_SecurityInComputerAndInformati\",\"cover\":\"http://192.168.1.102:5070/img/ComputerScience/978-3-319-95189-8_CoverFigure.jpg\",\"title\":\"Security in Computer and Information Sciences\",\"author\":\"Erol Gelenbe\",\"publisher\":\"Springer International Publishing\",\"bookId\":\"2018_Book_SecurityInComputerAndInformati\",\"category\":1,\"categoryText\":\"ComputerScience\",\"language\":\"en\",\"rootFile\":\"OEBPS/package.opf\",\"selected\":false,\"cache\":false,\"haveRead\":0,\"type\":1},{\"id\":8,\"fileName\":\"2018_Book_ComplicationsAndQuandariesInTh\",\"cover\":\"http://192.168.1.102:5070/img/Laws/2018_Book_ComplicationsAndQuandariesInTh.jpeg\",\"title\":\"Complications and Quandaries in the ICT Sector\",\"author\":\"Ashish Bharadwaj, Vishwas H. Devaiah and Indranath Gupta\",\"publisher\":\"Springer Singapore, Singapore\",\"bookId\":\"2018_Book_ComplicationsAndQuandariesInTh\",\"category\":9,\"categoryText\":\"Laws\",\"language\":\"en\",\"rootFile\":\"OEBPS/content.opf\",\"selected\":false,\"cache\":false,\"haveRead\":0,\"type\":1},{\"id\":-1,\"type\":3}]"}

but after I send it to the background, I print out only half the length, and then display undefined

axios Code:

app.post("/local", (req, res) => {
  req.on("data", data => { 
    // post
    let formData = decodeURIComponent(data)   // 
    // let param = qs.parse(formData)
    let param = querystring.parse(formData)   // object
    console.log(param.shelf)
  })
})

before querying some configurations (useless, only half of the data accepted by the server is printed.)

app.use(bodyParser.json({limit:"100mb"}));
app.use(bodyParser.urlencoded({ limit:"100mb", extended: true }));

I don"t know how to solve it. Has been bothering QAQ for a long time