To call router.push in Next.js as async, you can wrap it in a Promise and use the await keyword. Here's an example code snippet in JavaScript:

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const handleClick = async () => {
  await new Promise(resolve => router.push('/newRoute', undefined, { shallow: true }, resolve))
  // The code below this line will be executed only after the route changes
  console.log('Route changed successfully!')
}

In this example, the handleClick function is declared as async. Inside the function, we create a Promise that resolves when the route changes and wrap router.push in that promise. The await keyword is then used to wait for the Promise to resolve before executing the code below it. This ensures that we only log to the console after the route has changed successfully.

You can learn more about routing in Next.js in their official documentation here.

To pass a const string value from one page to another in Next.js as props without using a link, you can use the Router module.

First, you need to import the useRouter hook like this:

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import { useRouter } from 'next/router'

Then, you can use the push() method of the Router object to pass the const string value as a query parameter to the next page like this:

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const router = useRouter()

const handleClick = () => {
  const myConstString = "Hello World!"
  router.push({
    pathname: '/my-next-page',
    query: { myConstString },
  })
}

In the example above, the handleClick function is triggered when a button is clicked. It obtains the const string value and passes it to the my-next-page page as a query parameter using the Router.push() method.

Finally, in the my-next-page page, you can retrieve the const string value from the query parameter like this:

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import { useRouter } from 'next/router'

function MyNextPage() {
  const router = useRouter()
  const myConstString = router.query.myConstString

  //... rest of the code
}

In the example above, we are using the useRouter() hook again to get the myConstString value from the query parameter and use it in our component.

history.goBack() is a function in React Router that allows the user to navigate to the previous page in the browser history. If you want to define the state when using history.goBack(), you can pass the state object as a second argument to the history.push() method when navigating to the current page.

Here's an example code block in JavaScript:

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// defining state when navigating to current page
history.push('/current', { name: 'John' });

// go back to previous page
history.goBack();

In the above example, the current page is navigated to with the state object { name: 'John' }. When the history.goBack() method is called, the user will be taken to the previous page with the state from the '/current' page.

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import React, { useState } from 'react';
import { Link } from 'react-router-dom';

const Login = () => {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');

  return (
    <div className="login-page">
      <form>
        <h1>Login</h1>
        <label htmlFor="email">Email</label>
        <input
          type="text"
          name="email"
          value={email}
          onChange={(e) => setEmail(e.target.value)}
        ></input>

        <label htmlFor="password">Password</label>
        <input
          type="password"
          name="password"
          value={password}
          onChange={(e) => setPassword(e.target.value)}
        ></input>

        <button type="submit">Login</button>
      </form>
      <p>
        Don't have an account? <Link to="/register">Sign up</Link>
      </p>
    </div>
  );
};

export default Login;