JavaScript, how to exit a function

Nov 12, 2020

Learn how to exit a JavaScript function early using the return keyword, which stops execution immediately and can hand back a value or an error object.

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Sometimes when you’re in the middle of a function, you want a quick way to exit.

You can do it using the return keyword.

Whenever JavaScript sees the return keyword, it immediately exits the function and any variable (or value) you pass after return will be returned back as a result.

This is something I use all the time to make sure I immediately exit a function if some condition is not as I expect it.

Maybe I expect a parameter and it’s not there:

function calculateSomething(param) {
  if (!param) {
    return
  }

  // go on with the function
}

If the param value is present, the function goes on as expected, otherwise it’s immediately stopped.

In this example I return an object that describes the error:

function calculateSomething(param) {
  if (!param) {
    return {
      error: true,
      message: 'Parameter needed'
    }
  }

  // go on with the function
}

What you return depends on how the function is expected to work by the code that calls it.

Maybe you can return true if all is ok, and false in case of a problem. Or as I showed in the example above, an object with an error boolean flag, so you can check if the result contains this property (or a success: true property in case of success).

Tagged: JavaScript · All topics

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