Null check gotchas

📅 Aug 11, 2019 · 📝 Apr 30, 2020 · ☕ 1 min read

Beware of these null check gotchas.

Consider this code -

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const sum = null;

if (sum) {
  console.log("valid sum");
}

// nothing printed

The above code shows expected behaviour. Nothing is printed since if(sum) returns false.

Now, try the code below.

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if (sum >= 0) {
  console.log("valid zero or positive sum");
}

// valid zero or positive sum

It can throw off your calculations by a wide margin.

Strange but true null >= 0.

But, null > 0 and null == 0 both return false.

To work-around the problem always use the comparison directly in if statement or do an explicit Boolean conversion before the comparison.

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WRITTEN BY

Prashanth Krishnamurthy

Technologist | Creator of Things

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