This property returns ** the parent element ** of the current node. If there is no parent, it returns null.
The topmost parentElement in DOM is the `` element, which is also available as `document.documentElement`.
```js
let newEle = document.createElement("div");
newEle.parentNode // null
newEle.parentElement // null
// In case of appending to an element
document.body.append(newEle)
newEle.parentNode // ...
newEle.parentElement // ...
//In case of appending to a document fragment, say, df
df.append(newEle)
newEle.parentNode // document-fragment
newEle.parentElement // null
```
## Children
:::note Types of Children
All elements will *generally* have 2 types of children - an element or a text node.
You can think of elements as other tags and text node as the text within it.
```jsx
This is // <- 1. text node
// <- 2. element
some text // 2.1. text node
```
If you recall, *Element* extends from *Node* - so element and text node are both actually Node.
This is important because some properties return **only child elements**, whereas some return **all child nodes** (including text nodes).
For ex, `ele.childNodes` returns all child nodes, but `ele.children` returns only child elements.
**Always use the one which is more suitable for your case**. Remember, even if you haven't added any "text" between a tag, it can still have **invisible text nodes** due to spaces and newline characters.
```jsx
container.childNodes // [text, div, text]
// extra text nodes contain newline and space
```
Read more about [other types of nodes](https://developer.mozilla.org/en-US/docs/Web/API/Node/nodeType) and how [whitespace works in html](https://developer.mozilla.org/en-US/docs/Web/API/Document_Object_Model/Whitespace).
:::
### 3. children
`Element.children: HTMLCollection`
This property returns a live `HTMLCollection` containing all the **child elements** of the node. If there are no child elements, it returns empty HTMLCollection.
`HTMLCollection` can be converted to an array using `Array.from()` or `[...ele.children]`. HTMLCollection also has a `.length` property.
Here, the HTMLCollection is **live** - meaning if new child elements are added, they will automatically appear in this collection.
```jsx
Some text
some element
const children = parent.children;
children // HTMLCollection [span]
// 1. For-loop using .length
for (let i = 0; i < children.length; i++) {
console.log(children[i].tagName);
}
// 2. Convert to array
[...children].forEach(ele => {
// do something
})
```
This property is also available on `Document` and `DocumentFragment`.
:::note Counting number of child elements
`Element.childElementCount: number`
It returns the **number of child elements** of the given element. This is equivalent to `ele.children.length` value.
:::
### 4. childNodes
`Node.childNodes: NodeList`
This property returns a live `NodeList` containing all the **child nodes** of the current element. If there are no child nodes, it returns a empty NodeList.
`NodeList` can be converted to a array using `Array.from()` or `[...node.childNodes]`. NodeList also has a `.length` property.
Here, the NodeList is **live** - so the content of NodeList will auto-update.
```jsx
Some text
some element
and more text
const {childNodes} = parent;
childNodes // NodeList [text, span, text]
[...childNodes].forEach(node => {
// do something
})
```
This property is available on all types of `Node` - like Element, text node, etc.
:::note Check if there is any child node
`Node.hasChildNodes() : boolean`
This method checks whether the given node **has child nodes or not** and returns a boolean value. This is equivalent to checking `node.childNodes.length > 0`.
:::
### 5. firstChild + nextSibling
`Element.firstChild: Node`
This property returns the element's **first child** node in the tree. If there is no children, it returns `null`.
`Element.nextSibling: Node`
This property returns the node immediately **after the current one** in their parent's childNodes.
```jsx
let eleA = document.getElementById("A")
let eleB = eleA.firstChild //
let eleC = eleB.nextSibling //
eleC.nextSibling // null
```
There is also a similar `previousSibling` property which returns the previous node. Also, there are element-only variants like `firstElementChild`, `nextElementSibling`, etc.
:::note Easier traversal
This allows accessing the DOM tree in [Left-child right-sibling](https://en.wikipedia.org/wiki/Left-child_right-sibling_binary_tree) (LCRS) form, which is more memory efficient for usual traversal.
#### How do you implement dom traversal ?
The typical approach is to use a queue, push all children to the queue, pop them one-by-one and visit them. This requires **extra memory** because of the queue data structure which holds all the *next items to visit*.
But with the LCRS form, you always have access to the next item **without using extra space**. If current element has child, visit `.firstChild`. Then visit next node using `.nextSibling`.
```js
// 1. Typical approach
let queue = [root]
while (queue.length > 0) {
const item = queue.shift();
console.log(item);
if (item.hasChildNodes()) {
queue = queue.concat([...item.childNodes]);
}
}
// 2. LCRS approach
function traverse(item) {
if (item === null) {
return;
}
console.log(item);
traverse(item.firstChild)
traverse(item.nextSibling)
}
traverse(root.firstChild)
```
:::
## Content
### 6. innerText
`Element.innerText: string [= value]`
Returns the **text content** of the element and its descendants **"as rendered"**.
Can be set, to **replace the element's children** with the given string. It creates a *text node* for every normal text range, but replaces each line break with a `
` element.
**Example 1 -**
`.innerText` tries to return a string which represents the actual visible text, not the text literally written in html. Notice how <br/> tags and the css affects the output -
```jsx
Some text
then a newline
and another.
console.log(text.innerText)
// SOME TEXT
// THEN A NEWLINE
// AND ANOTHER.
```
:::note
On the other hand, `node.textContent` concatenates the actual text nodes used in the html and returns that string.
```jsx
console.log(text.textContent)
// Some text then a newline and another.
```
:::
**Example 2 -**
As setter, it replaces `\n` and `\r\n` in the input string with <br/> tags and wraps the rest in text nodes.
```jsx
text.innerText = "new text \n and a newline"
text.childNodes
// NodeList [
// text "new text ", br, text " and a newline."
// ]
// result html -
//
new text
and a newline
```
### 7. innerHTML
`Element.innerHTML: string [= value]`
Returns the **html markup contained within the element** as a string.
Can be set, to replace the **contents of the element with nodes parsed** from the given string. The existing content will be removed.
**Example 1-**
```jsx
console.log(parent.innerHTML)
//
text1
//
text2
```
**Example 2-**
```jsx
parent.innerHTML = `
text1
text2
`
// result html-
```
:::note To remove all children
To clear the content of any element, you can use `ele.innerHTML = ""`.
:::
### 8. outerHTML
`Element.outerHTML: string [= value]`
Returns the html markup of the **element and its contents** as a string.
Can be set, to **replace the element** itself with nodes parsed from the given string.
**Example 1-**
```jsx
console.log(parent.outerHTML)
//
```
**Example 2-**
Replacing `parent2` with 2 new nodes -
```jsx
parent2.outerHTML = `
child 1
child 2
`
// result html-
```
someImage.tagName // "IMG"
```
:::note Text nodes don't have `tagName`
Text nodes are not elements, so they don't have any tagName. To identify the type of node, use `.nodeType` property. For text nodes, `nodeType` is `3` - same as the constant `Node.TEXT_NODE`.
:::