Runtime errors occur when a program is running and encounters an unexpected condition.

Unlike syntax errors which are caught by the JavaScript parser, runtime errors occur during the execution of the program. Common examples of runtime errors include accessing undefined variables, performing operations on incompatible data types, or calling a function that doesn't exist.

To handle runtime errors and prevent the program from crashing, JavaScript provides a built-in mechanism called try-catch.

With try-catch, you can wrap the code that may throw an error in a try block, and catch the error in a catch block. This allows you to gracefully handle the error and continue with the execution of the program.

Let's take a look at an example:

1try {
2  // Example of a runtime error
3  const x = 1;
4  console.log(y);
5} catch (error) {
6  // Handle the error
7  console.error('An error occurred:', error);
8}

In the example above, we try to access the y variable which is not defined. This will throw a runtime error. However, since we have wrapped the code in a try-catch block, the error is caught and we can handle it by logging an error message to the console.

Using try-catch is a powerful tool for handling runtime errors and preventing them from crashing your program. It allows you to gracefully handle errors and provide fallback behavior or error messages to the user.

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// Example of a runtime error

const x = 1;

console.log(y);