How to Exit Functions in JavaScript

function addTwoNumbers(num1, num2) {
 return num1 + num2;
}

console.log(addTwoNumbers(5, 3)); // Outputs: 8

Using return statement

The ‘return’ statement in JavaScript ends function execution and specifies a value to be returned to the function caller. This concept can be better understood by looking at a simple example of a function that adds two numbers.

function addTwoNumbers(num1, num2) {
 return num1 + num2;
}

console.log(addTwoNumbers(5, 3)); // Outputs: 8

How it works

The ‘return’ statement used in the function ‘addTwoNumbers’ immediately stops the function and outputs the result of num1 + num2 to the location from where the function was called.

• The function ‘addTwoNumbers’ is defined with two parameters: ‘num1’ and ‘num2’.
• When the function is called, the arguments are passed in place of these parameters.
• The ‘return’ statement is encountered, which adds num1 and num2 and immediately exits the function, outputting the result to the caller of the function.
• In this case, the function is called within a ‘console.log()’ statement, so the output of the function (the sum of num1 and num2) is printed to the console.

By throwing an exception

We can halt execution of a JavaScript function by throwing an exception. This allows us to immediately exit the function when a certain condition is met. An example will help us understand this concept better.

function exitFunction() {
 try {
 // some code
 throw new Error('Exiting function due to an error');
 } catch(error) {
 console.error(error.message);
 }
}

How it works

The JavaScript throw statement allows us to create custom errors. When such an error is thrown, the function execution stops immediately, effectively exiting the function. The catch block then handles the exception.

• The function exitFunction() is declared.
• Inside the function, we have a try block where our main code resides. If any exception is thrown within this block, it gets caught by the subsequent catch block.
• The statement throw new Error('Exiting function due to an error'); throws an error, stopping the execution of the function.
• The function immediately exits and the control goes to the catch block.
• The catch block catches the thrown error and handles it. In this case, it logs the error message to the console.

By calling process.exit() in Node.js

process.exit() in Node.js is used to terminate a script or a function abruptly. It can be understood better with the following example where we will terminate a function based on a certain condition.

function doSomething() {
 let condition = true;
 if (condition) {
 console.log('Condition met. Exiting...');
 process.exit();
 }
 console.log('This will not run as the process has exited.');
}
doSomething();

How it works

When the process.exit() function is called, it causes the node.js runtime to end the process. If this function is used within a specific function or block, it results in the termination of that block and doesn’t allow the execution of any code that follows.

• The function doSomething is defined first.
• A variable condition is set to true.
• Next, an if statement checks whether condition is true.
• If the condition is met (which it is in this case), a message ‘Condition met. Exiting…’ is logged to the console.
• The process.exit() function is then called, which terminates the process. Any code following this call will not be executed. So the log message ‘This will not run as the process has exited.’ will not be printed to the console.
• Finally, the function doSomething is invoked.