Kevin Powell - Community•17mo ago

Cannot read properties of undefined.

Hello 👋 So I'm trying to create a class for an alert card. And now whenever i try to use the class methods it throws an error saying Cannot read properties of undefined ( reading 'classList') What am I missing here?

6 Replies

~MARSMAN~•17mo ago

https://codepen.io/ThatMartianDev/pen/KKBydVE

MarsMan

CodePen

Class undefined

...

~MARSMAN~•17mo ago

~MARSMAN~•17mo ago

And this is the error. I don't understand why when i console log the whole object it displays it with its every property. But when i use any of the class methods it says the element is undefined. I also tried to change the object class from outside of the Class by accessing the properties. and it throws the same error. So what am I missing here?

MarkBoots•17mo ago

when you create a card instance, you'll have to store it in a variable to be able to get access to it's methods and properties outside the class Also, a good practice is to name classes this a captital letter

const card = new AlterCard(alterItem)
card.showCard()
card.writeAlertContent()

const card = new AlterCard(alterItem)
card.showCard()
card.writeAlertContent()

also, if you want to access methods outside the class, they can not be static or private there were some other issues as well

class AlertCard {
  constructor(selector) {
    this.alertItem = document.querySelector(selector);
    this.alertContent = this.alertItem.querySelector("#alert-content");
    this.alertAnchor = this.alertItem.querySelector("#alert-anchor");
    this.closeBtn = this.alertItem.querySelector("#close-alert");
  }
  showCard() {
    this.alertItem.classList.add("show");
  }
  writeAlertContent(content) {
    this.alertContent.innerText = content;
  }
}

const card = new AlertCard("#alert");
card.showCard();
card.writeAlertContent("working");

class AlertCard {
  constructor(selector) {
    this.alertItem = document.querySelector(selector);
    this.alertContent = this.alertItem.querySelector("#alert-content");
    this.alertAnchor = this.alertItem.querySelector("#alert-anchor");
    this.closeBtn = this.alertItem.querySelector("#close-alert");
  }
  showCard() {
    this.alertItem.classList.add("show");
  }
  writeAlertContent(content) {
    this.alertContent.innerText = content;
  }
}

const card = new AlertCard("#alert");
card.showCard();
card.writeAlertContent("working");

i made it a bit cleaner by passing the id selector into the constructor function, so you dont have to select it first inside the constructor we select the element and the other parts you need

~MARSMAN~•17mo ago

Thank you so much Mark! It's working now 🙌 And thanks for the Tips!😊

MarkBoots•17mo ago

no problem. good luck!

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Cannot read properties of undefined.