UiQuestions/docs/create-modify-element.mdx

---
id: create-modify-element
# sidebar_label: DOM Manipulation
title: DOM Manipulation
slug: /
---

import Admonition from "../components/Admonition"
import Accordion from "../components/Accordion"
import MDN from "../components/MDNBadge"

## Finding elements

### 1. querySelector()

This method returns the **first element that matches the CSS selector**. If no match is found, it returns `null`.

```js
document.querySelector(selector);

// <div className="box" />
document.querySelector(".box"); // returns .box
document.querySelector(".not-found"); // null
```

<Accordion>
  <Admonition type="note" title="Extra">
  This method is also available on all DOM nodes. If you want to look within a specific element, this is very useful.

  ```js
  // Example - .outer > .inner
  outerEle.addEventListener((ev) => {
    var innerEle = ev.target.querySelector(".inner");
  });
  ```
  </Admonition>
</Accordion>

<MDN title="querySelector" url="https://developer.mozilla.org/en-US/docs/Web/API/Element/querySelector" />

### 2. querySelectorAll()

This method returns **all the elements that match** the specified CSS selector.

It returns a **static NodeList**, which contains the matching elements. If no match is found, it returns empty NodeList.

:::note How to consume NodeList?  
 NodeList is a iterable, so it can be iterated using `for..of` loop, or converted to a array using spread syntax like `[...nodelist]`.

Here, the NodeList is static - meaning any changes in the DOM later does not affect the content of the existing collection. More about NodeList [here](https://developer.mozilla.org/en-US/docs/Web/API/NodeList).  
:::

```js
var paras = document.querySelectorAll("p");

for (var p of paras) {
  p.className = "note";
}
```

<MDN title="querySelectorAll" url="https://developer.mozilla.org/en-US/docs/Web/API/Element/querySelectorAll" />

## Create / insert element

### 1. createElement()

It creates a new HTML element, taking the tag name (`"div"`) as argument.

```js
document.createElement("div")
// creates <div/>
```

<Accordion title="Related">
  <Admonition type="note" title="Creating text node">
    To add some text inside a element, you'll need to create a <b>text node</b>. 
    `createTextNode` method takes a string as input and returns a new TextNode.

  ```js
  var ele = document.createElement("div")
  var newText = document.createTextNode("Hello world")

  ele.appendChild(newText) 
  // <div>Hello world</div>
  ```
  </Admonition>
</Accordion>

<MDN title="createElement" url="https://developer.mozilla.org/en-US/docs/Web/API/Document/createElement" />

### 2. setAttribute()

It sets a attribute on the current element. 

`Element.setAttribute(name, value)`

`name` - name of the attribute to add. Ex- "type".  
`value` - value of the attribute. Ex- "text".

```js
var ele = document.createElement("input")

ele.setAttribute("type", "text") 
// <input type="text"/>
```
<MDN title="setAttribute" url="https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute" />


### 3. appendChild()

It inserts a new element as the last child of the parent element.

`Element.appendChild(newElement)`

```js
var eleDiv = document.createElement("div")
var eleH1 = document.createElement("h1")

eleDiv.appendChild(eleH1)
// <div><h1></h1></div>
```

<Accordion title="Edge cases and alternative">
  <Admonition type="note" title="If it already has a parent">
  If newElement is already a child of another element, 
  then it is removed from its existing parent and then added to the new parent.
  </Admonition>

  <Admonition type="note" title="If it is DocumentFragment">
  If newElement is a DocumentFragment, then - instead of adding the fragment itself as a child, 
  the entire content of the fragment is added as children of the parent element.
  </Admonition>

  <Admonition type="note" title=".append()">
  There is a newer api called .append(), which is a superset of .appendChild().<br/><br/>

  ⭐️ .append() allows you to insert multiple child elements in a single call. It also allows string as input, which gets converted to Text node.  

  ```js
  ele1.append(ele2, ele3, 'hello world')
  ```

  💔 .appendChild() only allows inserting a single element at a time.
  </Admonition>
</Accordion>

<MDN title="appendChild" url="https://developer.mozilla.org/en-US/docs/Web/API/Node/appendChild" />

### 4. removeChild()

`Element.removeChild(childElement)`

This method tries to remove a child element from the parent and returns the removed node.

If the element to be removed is not a child of the parent element, it throws a `NotFoundError` DOMException.

```js
// <div class="parent">
//   <div class="child"/>
// </div>

parentEle.removeChild(childEle)
```

<MDN title="removeChild" url="https://developer.mozilla.org/en-US/docs/Web/API/Node/removeChild" />

### 5. insertBefore()

`Element.insertBefore(newEle, refEle)`

This method inserts a new child element before another child within a parent.

`newEle` - The node to be inserted.  

`refEle` - The reference element before which newEle should be inserted. If refEle is `null`, then newEle is added as the last child.

```js
// <ul>
//   <li> Apple </li>
//   <li> Zebra </li>
// </ul>

// To add a new <li> above "Zebra"

var parent = document.querySelector("ul")
var ref = document.querySelector("li:last-child")

var newEle = document.createElement("li")

parent.insertBefore(newEle, ref)
```

:::note insertAfter()
There is no `insertAfter()` method. It can be emulated by combining insertBefore method with ele.nextSibling.

```js
parent.insertBefore(newEle, ref.nextSibling)
```
:::

<MDN title="insertBefore" url="https://developer.mozilla.org/en-US/docs/Web/API/Node/insertBefore" />

### 6. Document Fragment

DocumentFragment can be considered to be a off-screen lightweight `document` object. 
It is generally used for batching multiple operations - by doing them in the fragment over time and then rendering the whole content to the visible DOM in one shot .

Because fragment is not rendered, making changes to it doesn't cause any performance impact (no reflow).

**Methods** -

`document.createDocumentFragment()` - creates a new empty fragment.

`.appendChild()` / `.insertBefore()` - can be used to move the whole content of the fragment to the actual DOM.

**Example** -

```js
var fragment = document.createDocumentFragment()

// Insert / modify elements in fragment

// in dom, <div class="outer"/>
var outerEle = document.querySelector(".outer")

outerEle.appendChild(fragment)
// This will remove all content from fragment and 
// insert them within outerEle.

```

<MDN title="Document Fragment" url="https://developer.mozilla.org/en-US/docs/Web/API/DocumentFragment" />