having difficulty accessing the value within the Angular constructor

Question

having difficulty accessing the value within the Angular constructor

My current issue arises when I click on a button and set a value within the button click method. Despite declaring the variable in the constructor, I am unable to retrieve that value. The code snippet below demonstrates this problem as I keep getting 'undefined' in the constructor:

     public dat = {
  "pexels-photo.jpeg": {
    "information": "laptop",
    "desc": {
      "mimetype": "image/jpeg",
      "id": "shsj44",
      "file_id": "pexels-photo.jpeg"
    },
    "_id": "shsj44"
  }
};
  fileid= "";
  constructor(){
    console.log(this.fileid);

    // A URL HAS TO BE CALLED HERE WITH FILEID AS PARAMETER;
  }

  getData(){
   Object.keys(this.dat).forEach(key => {
      var value = this.dat[key];
      // console.log(key +':',value["_id"]);
      this.fileid = value["_id"];
      console.log(this.fileid);

    });
  }

You can find my code on StackBlitz here: https://stackblitz.com/edit/angular-dr7ehj

The reason why I declare this variable in the constructor is because I need to leverage its value for obtaining some information within the constructor.

javascript angular typescript

Answer 1

Answer №1

You did not define a variable in the constructor, you only logged the value of the variable in the constructor.

Since you are not assigning a value, you will receive undefined in the constructor. Please refer to the code below:

fileid='information';
  constructor(){
    console.log(this.fileid);
  }

  getData(){
    this.fileid = "infomation Updated";
    console.log(this.fileid);
  }

The updated information will be logged when clicking on a button.

Answer 2

You did not define a variable in the constructor, you only logged the value of the variable in the constructor.

Since you are not assigning a value, you will receive undefined in the constructor. Please refer to the code below:

fileid='information';
  constructor(){
    console.log(this.fileid);
  }

  getData(){
    this.fileid = "infomation Updated";
    console.log(this.fileid);
  }

The updated information will be logged when clicking on a button.

Answer 3

Answer №2

Everything is working as expected. The reason why the console.log is showing undefined is because you have not assigned a value to it, leading to its declaration without definition;

You can set an initial value either during declaration or within the constructor itself;

If your goal is to have 'information' logged on button click, then move your console.log statement to the getData() method so that it logs the updated fileId when the button is clicked.

Keep in mind that the constructor is only executed once, meaning if you wish to log after the button press, relocate the code to the getData method. If there are any services or other dependencies needed, they can be passed as private parameters to the constructor and accessed later in the getData method or elsewhere.

constructor(private service: MyService) {} // no action necessary in constructor

getData() {
    this.fileId = 'information'
    console.log(this.fileId);
    this.service(this.fileId); // or insert custom code here
}

You may also make use of ngOnChanges to trigger actions whenever a specific value changes

ngOnChanges(changes: SimpleChanges) {
    // utilize fileId as a parameter for a URL here
}

The issue with calling a URL in the constructor is that initially, the parameter is undefined, resulting in an invalid URL being sent initially.

Answer 4

Everything is working as expected. The reason why the console.log is showing undefined is because you have not assigned a value to it, leading to its declaration without definition;

You can set an initial value either during declaration or within the constructor itself;

If your goal is to have 'information' logged on button click, then move your console.log statement to the getData() method so that it logs the updated fileId when the button is clicked.

Keep in mind that the constructor is only executed once, meaning if you wish to log after the button press, relocate the code to the getData method. If there are any services or other dependencies needed, they can be passed as private parameters to the constructor and accessed later in the getData method or elsewhere.

constructor(private service: MyService) {} // no action necessary in constructor

getData() {
    this.fileId = 'information'
    console.log(this.fileId);
    this.service(this.fileId); // or insert custom code here
}

You may also make use of ngOnChanges to trigger actions whenever a specific value changes

ngOnChanges(changes: SimpleChanges) {
    // utilize fileId as a parameter for a URL here
}

The issue with calling a URL in the constructor is that initially, the parameter is undefined, resulting in an invalid URL being sent initially.

having difficulty accessing the value within the Angular constructor

Answer №1

Answer №2

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