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JavaScript

Posted by Gremyko Coleman
Gremyko Coleman
9,756 Points

How does const checkbox = e.target; know to target checkboxes on the ul.event handler for "change"?

In this section of code for const checkbox creates an input checkbox, 

const input = document.getElementById("name");
const form = document.getElementById("fanPage");
const ul = document.getElementById("list");

form.addEventListener("submit", (e) =>{
    e.preventDefault();

    let  text = input.value;        
    const li = document.createElement("li");
    const label = document.createElement("label");
    const checkbox = document.createElement("input");
          checkbox.type = "checkbox";

         li.appendChild(label);
         label.textContent = text;
         label.appendChild(checkbox);

        input.value = "";
        ul.appendChild(li);
        li.style.color = "blue";
});

But here, const checkbox = e.target; how does it target all checkboxes when the const checkbox in the above handler is on its own separate scope?

ul.addEventListener("change", (e)=>{
    const checkbox = e.target;  
    const checked = checkbox.checked; 
    const li = checkbox.parentNode.parentNode;
        if(checked){
            li.className = "select";
        }else{
            li.className = "";
        }
});

1 Answer

Steven Parker
Steven Parker
243,656 Points
Steven Parker
Steven Parker
243,656 Points

The listener is being placed on the "ul", so it will respond to any element inside it as the events "bubble up".

The reason only the checkboxes trigger the handler is because only input elements generate "change" events.

Gremyko Coleman
Gremyko Coleman
9,756 Points

Oooh, now it makes sense, because "change" only triggers input elements, thanks , Steven