Understanding Why console.log Outputs Twice in JavaScript

Discover why your string is being logged twice in a JavaScript if-else statement and learn effective solutions to fix the issue.
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The Problem Explained

You might have a block of code where you loop through an array of sentences and check their contents against certain conditions. Under certain scenarios, you may notice that the last string in the array is being logged twice, once as CURR0: and another time as PREV1:. The perplexity intensifies—why is this happening?

Here’s a look at a typical code snippet that raises this question:

[[See Video to Reveal this Text or Code Snippet]]

In this code, you're checking conditions on pairs of sentences (the current and previous). However, when you reach the last sentence, you expect only it to be logged under CURR0: Floating in ..., but it also triggers the logging as PREV1: Floating in .... Let's break down why this happens.

Why Does This Happen?

Modulus Operator Behavior

The underlying issue lies in the calculation of prevSentence. Consider how you implemented the logic:

[[See Video to Reveal this Text or Code Snippet]]

Here, the use of the modulus operator % ensures that when index reaches 0, it will refer to the last element of the array as prevSentence. This leads to the last string in your sentences being displayed both as a current sentence and as a previous sentence in the iteration.

How to Fix It

To prevent this double logging effect, you need to alter how the prevSentence is calculated, eliminating the reliance on the modulus operator. Here’s a simple fix using conditional logic:

[[See Video to Reveal this Text or Code Snippet]]

This means, when the index is 0 (the first sentence), prevSentence will be assigned an empty string instead of wrapping around to the last sentence. The code snippet modifies your loop logic below:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Debugging can sometimes lead to confusion, especially with conditional statements and array manipulations. Through understanding the mechanics behind the modulus operator and employing conditional checks, we can eliminate redundant logs and make our code cleaner and more efficient. By adjusting the prevSentence logic, as demonstrated, you can ensure that your code behaves as expected, with the correct logging in place.

Feel free to implement these changes in your own code, and happy coding!