Coding 3

**Link Component Navigation**
- To enable client-side navigation Next.js provides us with the Link component.
- The `<Link>` component is a React component that extends the HTML `<a>` element and is primary way for navigation
- To use it, we need to import it from 'next/link'.
Structure
```text
src/app
	blog
		page.jsx
	products
		page.jsx
	page.jsx
```
In `src/app/page.jsx`
```jsx
import Link from "next/link";

const Home = () => {
  return (
    <>
      <h1> Hello </h1>
      <Link href="/blog">Blog</Link>
      <Link href="/products">Products</Link>
    </>
  );
};

export default Home;

```
In `src/app/blog/page.jsx` `/` path is used to go to root page
```jsx
import Link from "next/link";

export default function Blog() {
  return (
    <>
      <h1>Blog</h1>
      <Link href="/">Home</Link>
    </>
  );
}

```
**For Dynamic Routes**
Structure
```text
src/app
	blog
		page.jsx
	products
		[productId]
			page.jsx
		page.jsx
	page.jsx
```
In `src/app/products/page.jsx`
```jsx
import Link from "next/link";

export default function ProductList() {
  const productId = 100;
  return (
    <>
      <h1>Product List</h1>
      <h2>Product 1</h2>
      <h2>Product 2</h2>
      <Link href={"products/3"} replace>
        {" "}
        <h2>Product 3</h2>{" "}
      </Link>
      <Link href={`products/${productId}`}>
        {" "}
        <h2>Product {productId}</h2>{" "}
      </Link>
    </>
  );
}

```
- Link for Dynmaic routes is generated just like we access the value of variable. 
  With `replace` keyword we can clear the url stack history means after navigating to `localhost:3000/products/3` and when we click back button we will navigate to `localhost:3000` not `localhost:3000/products`.
&nbsp;

**Active Links**
- First we need to create links for login, register, forgot-password in layout.jsx page for `(auth)`. So instead of creating these 3 links for each page ie login, register and forgot-password we used layout.jsx to serve this as template/same for all route groups.
Structure
```text
src/app
	(auth)
		login
		password
		forgot-password
		layout.jsx
	page.jsx
```
In `src/app/(auth)/layout.jsx`
```jsx
import Link from "next/link";

const navLinks = [
  { name: "Register", href: "/register" },
  { name: "Login", href: "/login" },
  { name: "Forgot Password", href: "/forgot-password" },
];

export default function OuterAuthLayout({ children }) {
  return (
    <div className="">
      {navLinks.map((link) => {
        return <Link href={link.href}>{link.name}</Link>;
      })}
      {children}
    </div>
  );
}

```
- So in order to style it we need to know the path of current url so we need to use the `usePathname` from 'next/navigation' hook. As we r using hook we need client side rendering for this and have to type `use client` at top in jsx file.
Structure
```text
src/app
	(auth)
		login
		password
		forgot-password
		layout.jsx
		style.css
	page.jsx
```
In `src/app/(auth)/layout.jsx`. Use the particular class for active link
```jsx
"use client";
import Link from "next/link";
import { usePathname } from "next/navigation";

import "./style.css";

const navLinks = [
  { name: "Register", href: "/register" },
  { name: "Login", href: "/login" },
  { name: "Forgot Password", href: "/forgot-password" },
];

export default function OuterAuthLayout({ children }) {
  const pathname = usePathname();
  return (
    <div className="">
      {navLinks.map((link) => {
        const isActive = pathname.startsWith(link.href);
        return (
          <Link
            href={link.href}
            key={link.name}
            className={isActive ? "active-link" : ""}
          >
            {link.name}
          </Link>
        );
      })}
      {children}
    </div>
  );
}

```
In `src/app/(auth)/style.css`
```css
a {
  margin: 0 1rem;
  color: blue;
}

a.active-link {
  color: black;
}

```
&nbsp;

**Navigating Programitically**
- Instead of using jsx, javascript can be used too so for that we can use the hook ie `useRouter` from 'next/navigation'.
Structure
```text
src/app
	order-product
		page.jsx
	page.jsx
```
In `src/app/order-product/page.jsx`
```jsx
"use client";
import { useRouter } from "next/navigation";

export default function OrderProduct() {
  const router = useRouter();
  const handleClick = () => {
    console.log("order placed");
    router.push("/");
  };

  return (
    <>
      <h1>Order Product</h1>
      <button onClick={handleClick}>Place Order</button>
    </>
  );
}

```
router.push('/') will push the root route to url stack and when we click on back after going through homepage it will brink back to the page `localhost:3000/order-product`. In `Link` coponent there was a attribute named replace which clears the url stack so to do same programitically use `router.replace('/')`.  Not only that but we can go to previous or next url stack too by `router.back()` and `router.forward()`
&nbsp;

**Templates**
- Templates are similar to layouts in the way they wrap each child layout or page 
  But with templates when  a user navigates between routes that share a template, a new instance of component is mounted, DOM elements are recreated, state is not preserved.
- So to only to be used once we dont have to conserve states and need a template to recreate pages so their states dont conflict with each other
Without template
```text
src/app
	(auth)
		login
		password
		forgot-password
		layout.jsx
		style.css
	page.jsx
```
In `src/app/(auth)/layout.jsx`
```jsx
"use client";
import Link from "next/link";
import { usePathname } from "next/navigation";

import "./style.css";

import { useState } from "react";

const navLinks = [
  { name: "Register", href: "/register" },
  { name: "Login", href: "/login" },
  { name: "Forgot Password", href: "/forgot-password" },
];

export default function OuterAuthLayout({ children }) {
  const pathname = usePathname();
  const [input, setInput] = useState("");

  return (
    <div className="">
      <div className="">
        <input
          type="text"
          value={input}
          onChange={(e) => setInput(e.target.value)}
        />
      </div>
      {navLinks.map((link) => {
        const isActive = pathname.startsWith(link.href);
        return (
          <Link
            href={link.href}
            key={link.name}
            className={isActive ? "active-link" : ""}
          >
            {link.name}
          </Link>
        );
      })}
      {children}
    </div>
  );
}

```
When we move to new route input will be same and wont be reset. 
**With templates**
Just change the file name from layout.jsx to template.jsx and now input will be reset and nothing will be preserved.
Some limitations though. If there is a route group(say named inner-auth) like this
Structure
```text
src/app
	(auth)
		(inner-auth)
			login
			password
		forgot-password
		template.jsx
		style.css
	page.jsx
```
In this case, states between `login` and `password` routes will be shared not with `forget-password` route though.
&nbsp;

**Loading UI**
- Till now different files like `page.jsx`, `layout.jsx`, `not-found.jsx` and `template.jsx` have been used. There is another one ie `loading.jsx`.
Structure
```text
src/app
	blog
		first
		second
		loading.jsx
		layout.jsx
		page.jsx
	page.jsx
```
In `src/app/blog/loading.jsx`
```jsx
export default function LoadingBlog() {
  return (
    <div className="LoadingBlog">
      <h1>Loading</h1>
    </div>
  );
}

```
To test it, make sure that `src/app/blog/page.jsx` loads slower due to setTimeout. Make sure that layout.jsx wont load slow as first layout.jsx is loaded then loading.jsx contents then page.jsx.

In `src/app/blog/page.jsx`
```jsx
import Link from "next/link";

export const metadata = {
  title: {
    absolute: "blog",
    default: "blog",
  },
};

function promiseSetTimeOut(time) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve();
    }, time);
  });
}

export default async function Blog() {
  await promiseSetTimeOut(1000);
  return (
    <>
      <h1>Blog</h1>
      <Link href="/">Home</Link>
    </>
  );
}

```