When I try to make ID ; "Cannot read property 'length' of undefined."

Question

Dear all; I was not sure if I should also share my html project. Im stuck here :/ I have checked few questions similar to that but no solution yet...

I wanted to make ID which should be different always but could not end up my problem.

Uncaught TypeError: Cannot read property 'length' of undefined Please help me about it : Uncaught

TypeError: Cannot read property 'length' of undefined at Object.addItem (app.js:30) at kontrolEkle (app.js:112) at HTMLDocument. (app.js:97)

//Price Budget Control var butcekontrol = (function(){

   var Giderler = function(id,aciklama,deger){
       this.id=id;
       this.aciklama=aciklama;
       this.deger=deger;
   };
   var Gelirler = function(id,aciklama,deger){
       this.id=id;
       this.aciklama=aciklama;
       this.deger=deger;
   };
   var data = {
       tumislem:{
           gelir: [],
           gider: []
       },
        toplam: {
           gelir:0,
           gider:0
       }
   }

when I return here :

       return{   
       addItem: function(type,des,val){
       var newItem,ID;
        // YENİ ID OLUŞTURMA   
        if (data.tumislem[type].length > 0) {
                ID = data.tumislem[type][data.tumislem[type].length - 1].id + 1;
            } else {
                ID = 0
            }
        // Tipine Göre Ekleme Çıkarma Yapma
       if(type==='exp'){
        newItem = new Giderler(ID , des , val)
       } else if(type==='inc'){
           newItem = new Gelirler(ID , des, val)
       }
       // Dataya Push İşlemi Yapma       
      data.tumislem[type].push(newItem);
           // RETURN//
           return newItem;
     },
        testing:function(){
            console.log(data);}
  };               

})();

User Interface Control Code Area

    var arayuz = (function(){
    var Domstrings = {
        InputType:'.add__type',
        InputDescription:'.add__description',
        InputValue:'.add__value',
        InputBtn:'.add__btn',

    };

       return {
        getInput: function() {
            return {
                type: document.querySelector(Domstrings.InputType).value, // Will be either inc or exp
                description: document.querySelector(Domstrings.InputDescription).value,
                value: document.querySelector(Domstrings.InputValue).value
            };
        },

           getDomstrings:function(){
               return Domstrings;
           }

     }

})();

And last part

    var kontrol = (function(butceknt,arayz){
    var setupcontroller = function(){
       //KODLAR BURAYA
        var DOM = arayuz.getDomstrings();
     document.querySelector(DOM.InputBtn).addEventListener('click',kontrolEkle);

        document.addEventListener('keypress', function(tik){
            if(tik.keyCode===13){
               kontrolEkle();
            }})

        //END Of the line 

    }

 var kontrolEkle = function(){
    //1. Formlardan Değer Alma
    var input,addItem;

     input = arayuz.getInput();
        console.log(input);
    //2.Bütçe Kontrole Ekleme

     addItem = butcekontrol.addItem(input.type,input.description,input.value);
    //3.Kullanıcı Arayüzünde Güncelleme

    //4.Bütçeyi Hesaplama

    //5.Kullanıcıya Son Bütçeyi Gösterme

    }
return{
    init:function(){
        console.log('Application Started');
        setupcontroller();
    }
}


})(butcekontrol,arayuz);

kontrol.init();

Answer 1

发生这种情况是因为你试图获取 undefined 的长度，你能确保 data.tumislem[type].length 返回值，通过 console.log 吗？

Answer 2

Hey man I think this line is the issue.

ID = data.tumislem[type][data.tumislem[type].length - 1].id + 1;

data.tumislem[type] is coming back as null or undefined , check there first.