Exit Function in JavaScript

When creating a function using JavaScript, you may want to stop its execution and exit it. To do so, these are two ways of doing it:

• by reaching the function end
• by using the return statement. Once your program reaches this instruction, it will exit the function by returning a value.

Exit a JavaScript function by reaching its end

Before discovering how to exit in JavaScript, let's see when a function exits by itself.

Here is an example:

function writeMyName(name) {
  // Print the name variable
  console.log(name)
  // Then, reach the end of the function
  // and automatically exit it
}

writeMyName('Gaël')

// Output: "Gaël"

In the case above, you have a simple example. As you can see, the function only prints the name variable. In that case, the program exit the function after executing all the instructions.

Return in JavaScript function

Exit and return an undefined value

Now, let's dig a bit further and see how you can exit a function using the return statement. This statement allows you to leave a function once you reach it.

Let me show you an example:

function writeMyName(name) {
  // Execute the return instruction
  // and automatically exit the function
  // Note: all code after a `return` isn't executed
  return
  // Print the name variable
  console.log(name)
}

writeMyName('Gaël')

// No output

By default, the return statement send an undefined value. As an example, if you save the writeMyName output to a variable and print it, here what you will get:

function writeMyName(name) {
  // Execute the return instruction
  // and automatically exit the function
  // Note: all code after a `return` isn't executed
  return // No value = undefined
  // Print the name variable
  console.log(name)
}

const output = writeMyName('Gaël')

console.log(output)

// Output: undefined

Exit and return a value

Now, you know how to stop a function and exit it whenever you want. But, let's imagine that you want to exit a JavaScript process and send a result value.

You can do the same as we did before, but specify a value. This value can come from a variable.

function writeMyName(name) {
  if (name === 'Wrong') return false

  // Print the name variable
  console.log(name)

  return true
}

console.log(writeMyName('Gaël'))

// Output:
// "Gaël"
// true

console.log(writeMyName('Wrong'))

// Output: false

In the example above, you're first checking the name variable value. If the value is "Wrong", you exit the function and send a false boolean value. Otherwise, you print the name variable, then send a true boolean value as a return value.

That's all about how you can exit a JavaScript function. 🚀