Kevin Powell - Community•5mo ago

querySelectorAll not working

Hi everyone I realise this : https://codepen.io/alpha_66/pen/MWxoLZJ the problem appear when I use querySelectorAll to select all li tag I get this message if I just use querySelector('li'); is working but only for one element can I some idea about how to fix this problem ? thanks

Patrick L

CodePen

MWxoLZJ

...

16 Replies

Jochem•5mo ago

That one returns an array, you have to loop over the array and add listeners to each record yourself.

Jochem•5mo ago

https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelectorAll#accessing_the_matches

MDN Web Docs

Document: querySelectorAll() method - Web APIs | MDN

The Document method querySelectorAll() returns a static (not live) NodeList representing a list of the document's elements that match the specified group of selectors.

Caps-look•5mo ago

for(let i=0; i<couleur.length;i++){
    couleur[i].addEventListener(/*...*/);
    /*...*/
}

for(let i=0; i<couleur.length;i++){
    couleur[i].addEventListener(/*...*/);
    /*...*/
}

Jochem•5mo ago

you forgot ; i++ in the for loop descriptor

Caps-look•5mo ago

thanks

Pat66•5mo ago

I try like this :

 const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur[i].addEventListener("mouseover",()=>{
            couleur.classList.add('ch');
            console.log('pat66');
        })

      }

 const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur[i].addEventListener("mouseover",()=>{
            couleur.classList.add('ch');
            console.log('pat66');
        })

      }

Pat66•5mo ago

I have this message :

Jochem•5mo ago

couleur[i].classList.add might work

Pat66•5mo ago

the new one:

  const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur.addEventListener("mouseover",()=>{
            couleur[i].classList.add('ch');
            console.log('pat66');
        })


        couleur[i].addEventListener("mouseout",()=>{
            couleur[i].classList.remove('ch');
            console.log('pat66');
        })

      }

  const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur.addEventListener("mouseover",()=>{
            couleur[i].classList.add('ch');
            console.log('pat66');
        })


        couleur[i].addEventListener("mouseout",()=>{
            couleur[i].classList.remove('ch');
            console.log('pat66');
        })

      }

now I have :Uncaught TypeError: couleur.addEventListener is not a function

Jochem•5mo ago

you didn't add [i] to the first addEventListener

Pat66•5mo ago

OK I had it

Pat66•5mo ago

  const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur[i].addEventListener("mouseover",()=>{
            couleur.classList.add('ch');
            console.log('pat66');
        })


        couleur[i].addEventListener("mouseout",()=>{
            couleur.classList.remove('ch');
            console.log('pat66');
        })

      }

  const couleur=document.querySelectorAll("li");
         //  console.log(couleur);

      for(let i=0;i<couleur.length;i++){

        couleur[i].addEventListener("mouseover",()=>{
            couleur.classList.add('ch');
            console.log('pat66');
        })


        couleur[i].addEventListener("mouseout",()=>{
            couleur.classList.remove('ch');
            console.log('pat66');
        })

      }

Jochem•5mo ago

I'd recommend reading up on how for loops and scope work. You're looping over couleur, one by one, but that doesn't change the value of couleur. Inside the for loop, you can access the children of couleur by adding [i]. You're indexing into the array of couleur, going to index i, and access that particular child when you read those errors, they say exactly what's wrong. You're trying to access the property add or remove on the classList property of the array couleur, which doesn't have a classList property, so it's producing an error it says "cannot read properties of undefined (reading 'add')" because couleur.classList is undefined on an array. In this particular array, it is accessible on its children though I'd recommend trying to figure this one out on your own, based on ^ that, but if you want to have the solution You just need to add [i] to the couleur in the two event listeners

MarkBoots•5mo ago

btw, different from the question how to do the loops. you are adding/removing the same class on mouse over and mouse out. you do know you can use css hover?

li:hover{ 
  background-color: green; 
}

li:hover{ 
  background-color: green; 
}

Pat66•5mo ago

thanks for your message but the exercise need JS

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querySelectorAll not working