ArticleZip > Chrome Firefox Console Log Always Appends A Line Saying Undefined

Chrome Firefox Console Log Always Appends A Line Saying Undefined

Have you ever noticed that when you're debugging your code in Chrome or Firefox, the console log always seems to add an extra line that says "undefined"? Don't worry, you're not alone! This issue can be quite common when working with JavaScript, but luckily, there's an easy fix for it.

The reason why you see "undefined" in the console log is that when you use console.log() to output a message, the function itself doesn't return anything. So, if you were to log the result of an operation that doesn't have a value, like:

Plaintext

console.log(5 + 'undefined');

The browser will log the result of the operation, but since there is no return value from the console.log() function, it will automatically append "undefined" to the next line.

To prevent this from happening and keep your console log clean, you can simply add a return statement after the console.log() function call, like this:

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console.log(5 + 'undefined');
return;

Adding return; at the end of your console.log() statement will prevent the browser from automatically adding "undefined" on the next line.

Another approach to avoid the extra "undefined" line is to explicitly return a value from the function where you are using console.log(). For example:

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function add(a, b) {
  const result = a + b;
  console.log(result);
  return result;
}

add(3, 4);

By explicitly returning a value from the function, you ensure that the console.log() call does not leave an "undefined" line in the console log.

Moreover, you can also use a simple if statement to check if the console.log() statement has any output before returning. This way, you can prevent the "undefined" line from being added when there is no actual output in the console log:

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function printIfValueExists(value) {
  if (value) {
    console.log(value);
  }
  return;
}

printIfValueExists(null);
printIfValueExists('Hello, world!');

In conclusion, dealing with the extra "undefined" line in the console log is a common issue that many developers face. By understanding how the console.log() function works and implementing simple solutions like adding a return statement or checking for output before returning, you can keep your debugging experience in Chrome and Firefox nice and clean.

Next time you encounter this problem, remember these easy tips to prevent that pesky "undefined" from cluttering up your console log. Happy coding!

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