如何将元素添加到 javascript 中的 HTMLCollection 中？

Question

I have an HTMLCollection Object which i can use to manipulate the content of the HTMLCollection. I would like to know the way out to add a div element to the first, last or to any specific index of the HTMLCollection. Please suggest something. Here nDivs is the HTML Collection.

    var Div = document.createElement('div');
    for(i=0; i<9; i++){
        Div.appendChild(nDivs[0].children[0]);
    }
    Div.id = nDivs[0].id;
    nDivs[0].parentNode.removeChild(nDivs[0]);

    nDivs.appendChild(Div); //this is creating problem..need an alternative to this
    document.getElementById("ABC").appendChild(nDivs[nDivs.length - 1]);

Answer 1

According to the MDN docs

HTMLCollection is an interface representing a generic collection of elements (in document order) and offers methods and properties for traversing the list.

Because its an interface, you're restricted to interacting with an HTMLCollection via its methods . There are no methods there to modify the object, only to read it. You'll have to manipulate the DOM some other way .

Here are some suggestions using pure JS, but I highly recommend jQuery for such tasks. Assume we're working with a new element newDiv and the HTMLCollection document.forms :

insert before forms[1] :

forms[1].parentNode.insertBefore(newDiv, forms[1]);

insert after forms[1] :

// there is no insertAfter() so use the next sibling as reference element
forms[1].parentNode.insertBefore(newDiv, forms[1].nextSibling);

replace forms[1] :

forms[1].parentNode.replaceChild(newDiv, forms[1]);

Documentation and examples for insertBefore() , replaceChild() , nextSibling , and parentNode .

Answer 2

You need to insert your new Elements in the DOM directly. You cannot manipulate a read-only HTMLCollection directly. But don't worry, your HTMLCollection (stored in a variable) will update accordingly:

 // DOM helper functions: const el = (sel, par) => (par || document).querySelector(sel); const elNew = (tag, prop) => Object.assign(document.createElement(tag), prop); // Cache a reference to the wrapper parent Element const elParent = el("#parent-a"); // Cache a live HTMLCollection: const collItems = elParent.children; // Insert new elements in the DOM: elParent.prepend(elNew("div", {textContent: "Item First (New)"})); elParent.append(elNew("div", {textContent: "Item Last (New)"})); // Check if the collection is live: console.log(collItems.length); // 5

 <div id="parent-a"> <div class="item">Item 1</div> <div class="item">Item 2</div> <div class="item">Item 3</div> </div>

as you can see above (contrary to if you used ie: const collItems = elParent.querySelectorAll(".item"); ) the live HTMLCollection reports that is has 5 children in total.

Also, you can see how to append and prepend an item as first or last .
To answer your other question:

"how to insert at a specific index"

you can use:

 // DOM helper functions: const el = (sel, par) => (par || document).querySelector(sel); const elNew = (tag, prop) => Object.assign(document.createElement(tag), prop); const insertAtIndex = (idx, parent, ...els) => { els = els.flat(); const ch = parent.children; if (idx >= ch.length) parent.append(...els); else ch[Math.max(idx, 0)].before(...els); }; // Cache a reference to the wrapper parent Element const elParent = el("#parent-a"); // Cache a live HTMLCollection: const collItems = elParent.children; // Insert element/s at index insertAtIndex( 2, elParent, elNew("div", {textContent: "NEW item 1"}), elNew("div", {textContent: "NEW item 2"}), ); console.log(collItems.length); // 4

 <div id="parent-a"> <div class="item">Item 1</div> <div class="item">Item 2</div> <div class="item">Item 3</div> </div>