This article covers

1. Difference between HTMLCollection and NodeList
2. item & namedItem method of HTMLCollection
3. Iterating HTMLCollection.
4. item, values, keys, entries, forEach method of NodeList

HTMLCollection vs NodeList

HTMLCollection is a Dynamic List of Objects of elements whereas the NodeList is static.

For instance

<p> Hii </p>
<p> What's your name ? </p>
<script>
let dynamicCollection = document.getElementsByTagName('p'); 
//returns HTMLCollection
console.log(dynamicCollection);

let staticCollection = document.querySelectorAll('p');
//returns NodeList
console.log(staticCollection)
</script>

Output

Here Both have two <p> elements in the list.

Now let us create another <p> element with DOM.

let additionalP = document.createElement('p');
additionalP.innerHTML = "Where do you live? ";

document.body.appendChild(additionalP);

Now let us again console.log both variables holding the list of <p> elements.

console.log(dynamicCollection);
console.log(staticCollection)

Output:

Now see here, The HTMLCollection is updated automatically while NodeList stays the same. This is the key difference.

HTMLCollection methods

1. item

You can access the members of HTMLCollection i.e element's object, using the item method. It expects the index of the element as a parameter.

console.log(dynamicCollection.item(0));

output

2. namedItem

namedItem expects a parameter and returns the element having id or name given in the parameter.

For example

<p id='greeting'>Hii </p>
<p> How are you </p>

<script>
let elems = document.getElementsByTagName('p');
console.log(elems.namedItem('greeting'));
<script>

Output

HTMLCollection Iterations

You can iterate through each member of HTMLCollection using for loop.

let elements = document.getElementsByTagName('p');

for(let i = 0; i < elements.length; i++){
console.log(elements[i]);
}

NodeList Methods

1. Item

same as HTMLCollection.

let p = document.querySelectorAll('p');
p.item(0); //returns first member of list 

//alternative
p[0] //same as p.item(0)

2. entries

<p>Hii</p>
<p>What's your name ? </p>
<script>
let p = document.querySelectorAll('p');
for(let entry of p.entries()){
    console.log(entry);
}
</script>

Output

entry is an array with [index, element] as shown above

3. keys

<p>Hii</p>
<p>What's your name ? </p>
<script>
let p = document.querySelectorAll('p');
for(let key of p.keys()){
    console.log(key);
}
</script>

Output

Here key is just the key of a member of HTMLCollection.

4. values

<p>Hii</p>
<p>What's your name ? </p>
<script>
let p = document.querySelectorAll('p');
for(let value of p.values()){
    console.log(value);
}
</script>

Output Here value is the member of HTMLCollection.

5. forEach

<p>Hii</p>
<script>
let p = document.querySelectorAll('p');

p.forEach(function(value,index,nodeList){
    console.log(value);
    console.log(index);
    console.log(nodeList);
    console.log(this);
},'anythingYouWantToReferAsThisInsideTheLoops');

</script>

Output: The picture is really worth a thousand words, ain't it?

Hope you got a clear understanding of HTMLCollection and NodeList and their differences. If not, comment your query.