The prompt() function is a built-in function in JavaScript that displays a dialog box to the user with a message to enter some input. The user can then enter a value into the dialog box and click "OK" or "Cancel".

Here is an example of how it can be used:

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let name = prompt("Please enter your name:");
console.log("Hello, " + name + "!"); 

This code will display a dialog box to the user with the message "Please enter your name:". The user can enter their name and click "OK" to store the value in the name variable. The code then logs a greeting message to the console using the entered name.

You can find more information about the prompt() function here.

Here's an example of a JavaScript alert code:

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alert("Hello World!"); 

This will display a message box in the browser with the text "Hello World!" inside it.

It's worth noting that Java and JavaScript are two different programming languages and they have different syntax and uses. If you were asking for Java alert code (not JavaScript), I'm assuming you were referring to JOptionPane. Here's an example:

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import javax.swing.JOptionPane;

public class Main {
  public static void main(String[] args) {
    JOptionPane.showMessageDialog(null, "Hello World!");
  }
}

This will display a message box in a Java program with the text "Hello World!" inside it. The JOptionPane class provides many other types of dialogs as well that you can use in your Java programs. You can learn more about it here: https://docs.oracle.com/javase/tutorial/uiswing/components/dialog.html

To use prompt and alert in JavaScript, you can follow the examples below:

prompt is used to display a dialog box that asks the user for input. The user can enter text and then click OK or Cancel. Here's an example of how to use prompt:

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let name = prompt("What is your name?");
console.log(`Hello, ${name}!`);

In this example, a dialog box will appear asking the user for their name. The name is stored in a variable called name and then printed to the console.

alert is used to display a message box to the user. Here's an example of how to use alert:

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alert("Hello, world!");

In this example, a message box will pop up with the text "Hello, world!"

Note that prompt and alert are both functions that are built into JavaScript and do not require any libraries or additional setup.

The main difference between alert() and console.log() in JavaScript is that alert() is a method of the window object and console.log() is a method of the console object.

alert() function displays a message box with a specified message and an OK button. It halts the further execution of the code until the user presses the OK button.

console.log() function is used for printing some output to the console. It does not block the execution of further code and does not require user interaction.

Example:

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alert('Hello World!');
console.log('Hello World!');