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Asked: 2024-09-22T03:06:33+05:30 In:

When deciding between using the nullish coalescing operator and the logical OR operator in JavaScript, what factors should I consider? In what scenarios is one preferable over the other for handling undefined or null values?

Hey everyone! I’ve been diving into JavaScript lately and got a bit tangled up with the nullish coalescing operator (`??`) and the logical OR operator (`||`). I understand that both can be used to handle undefined or null values, but I’m unsure when to use one over the other.

For example, I know that `??` only checks for `null` or `undefined`, while `||` also considers other falsy values like `0`, `NaN`, and empty strings.

Could anyone share their experiences or insights on this? In what specific scenarios have you found one to be more useful than the other? I’d love to hear some examples or potential pitfalls to watch out for!

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    3 Answers



    1. JavaScript Nullish Coalescing vs Logical OR

      The nullish coalescing operator (`??`) and the logical OR operator (`||`) serve different purposes in JavaScript, and understanding their distinctions can enhance your coding efficiency. The `??` operator is particularly useful when you want to provide a default value only in the case that the left-hand operand is either `null` or `undefined`. This means it maintains falsy values such as `0`, `NaN`, or empty strings, allowing them to be treated as valid inputs. For instance, when dealing with configurations or optional parameters in functions, you might want to default a value only when no value has been explicitly passed (i.e., it’s `undefined` or `null`). In contrast, using `||` would force a fallback to a default value in situations where the left operand could be any falsy value, which may not always be the desired behavior.

      One specific scenario where I’ve found `??` to be exceptionally useful is while dealing with numerical inputs. Consider a function that takes a user input that may include zero; if you use `||`, then any input of `0` will trigger the fallback, potentially leading to logic errors. For example, `const someValue = userInput || defaultValue;` will incorrectly evaluate to `defaultValue` if `userInput` is `0`. In contrast, using `??` will correctly allow `0` to pass through. However, caution is necessary when making assumptions about how these operators will process multiple levels of nested values or complex conditions, as their behavior can lead to unexpected outcomes if not carefully considered.







    2. JavaScript Nullish Coalescing vs Logical OR

      Understanding Nullish Coalescing (`??`) vs Logical OR (`||`)

      Hey there! It’s great that you’re exploring JavaScript and diving into the nuances of these operators. You’re right that both the nullish coalescing operator and the logical OR operator are used to provide default values, but their behaviors differ in important ways.

      Differences:

      • Nullish Coalescing Operator (`??`):

        This operator only checks for null and undefined. It does not consider other falsy values like 0, NaN, or empty strings as reasons to provide a default value.

      • Logical OR Operator (`||`):

        This operator will return the right-hand side value if the left-hand side value is any falsy value, including 0, NaN, "" (empty string), false, and null/undefined.

      When to Use Which:

      Choosing between these operators depends on your specific requirements:

      • Use ?? when:

        You want to assign a default value only if a variable is null or undefined. For example:

        const x = null;
const value = x ?? 'default'; // value will be 'default'
      • Use || when:

        You want to assign a default value when a variable is any falsy value. For example:

        const x = 0;
const value = x || 'default'; // value will be 'default'

      Potential Pitfalls:

      Be cautious when using || because it can lead to unexpected behavior if you are working with values like 0 or empty strings that you wish to keep. For instance:

      const count = 0;
const total = count || 10; // total will be 10, but you might want to keep 0

      In contrast, using ?? would preserve the value:

      const count = 0;
const total = count ?? 10; // total will be 0

      Conclusion:

      In summary, choose ?? when you specifically want to handle null and undefined, and go with || when you want to address all falsy values. Hope this helps clarify things for you! Happy coding!


    3. Understanding Nullish Coalescing (`??`) vs Logical OR (`||`)

      Great question! I’ve definitely been in that situation where I had to choose between using the nullish coalescing operator and the logical OR operator in JavaScript.

      When to use `??`

      The nullish coalescing operator (`??`) is particularly useful when you want to provide a default value only if the original value is null or undefined. This is handy when you want to allow for other falsy values, such as 0, NaN, or an empty string to be treated as valid inputs.

      For example:

      
const value = 0;
const result = value ?? 10; // result is 0

      When to use `||`

      On the other hand, the logical OR operator (`||`) checks for any falsy values. This includes false, 0, NaN, empty strings, as well as the usual null and undefined. Use it when you want to provide a default value for anything that evaluates to falsy.

      For example:

      
const value = 0;
const result = value || 10; // result is 10

      Potential Pitfalls

      A common pitfall I encountered was using `||` when I wanted to handle undefined or null only, leading to unexpected results. For example:

      
const userInput = ""; // user didn't enter anything
const userName = userInput || "Guest"; // userName is "Guest"
const anotherUserName = userInput ?? "Guest"; // anotherUserName is ""

      As you can see, using `||` here replaced the empty string with “Guest,” while `??` preserved the empty string.

      Conclusion

      In summary, choose `??` when you only want to check for `null` or `undefined`, and opt for `||` when you’re okay with any falsy value triggering the default. Knowing the difference can save you from a lot of headaches down the line!

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