Class attribute in constructor

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Class attribute in constructor

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#1 by (0 votes)

1

I can access an attribute of the class within the scope of the constructor, however outside gives ' undefined '

constructor(errorAlert){
  this._errorAlert = errorAlert;
}

If, for example, in the code above, I give% of the% in the parameter received and the attribute, both return the same value, but when I use the attribute in the rest of the class, I can not.

class Controller{
  constructor(errorAlert){
    this._errorAlert = errorAlert;
  }
  login(login, senha){
    let $ = new Serv();
    $.ajax({
      'url': '/login',
      'type': 'post',
      'responseType': 'json',
      'data': 'login='+login+'&senha='+senha
    }).then(function(resolve){
      let datas = resolve;
      if(datas['loginStatus'] == 1){
        window.location = base_url;
      }else{
          console.log(this._erroAlert);
          view.viewErrorMessage("Usuário ou senha incorreto", this._errorAlert);
      }
    }).catch(function(reject){
      console.log(reject);
    });
  }
}

The code works perfectly, my only problem is that of the scope of the same attribute.

Error:

TypeError: Cannot read property '_erroAlert' of undefined
    at Controller.js:19
    at <anonymous>

javascript ecmascript-6 construtor

asked by anonymous 30.10.2017 / 17:59

1 answer

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score 0 · Accepted Answer

The problem is that when you run an anonymous function within your class, the this reference is no longer for your object, but for the AJAX request object defined by $.ajax of jQuery. That is, when you do this._errorAlert you are trying to access the _errorAlert attribute of your request, which does not exist.

To get around this in an easy way, you can save the% object of% of your instance to another variable before doing the asynchronous request:

const self = this;

And within the anonymous function, do:

console.log(slef._erroAlert);

Getting something like:

class Controller{
  constructor(errorAlert){
    this._errorAlert = errorAlert;
  }
  login(login, senha){
    let $ = new Serv();
    const self = this;    // Linha adicionada
    $.ajax({
      'url': '/login',
      'type': 'post',
      'responseType': 'json',
      'data': 'login='+login+'&senha='+senha
    }).then(function(resolve){
      let datas = resolve;
      if(datas['loginStatus'] == 1){
        window.location = base_url;
      }else{
          console.log(self._erroAlert);    // Linha modificada
          view.viewErrorMessage("Usuário ou senha incorreto", self._errorAlert);    // Linha modificada
      }
    }).catch(function(reject){
      console.log(reject);
    });
  }
}