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Exercise 10

Challenging Exercise This exercise has nothing to do with this chapter. Instead, it uses concepts you learned earlier in the book. If you can't figure out the answer, don't worry: this question can stump developers with more experience than you have.

Consider this code:

> let x = "5"
> x = x + 1
= "51"

Now, consider this code:

> let y = "5"
> y++

What gets returned by y++ in the second snippet, and why?

Solution

The return value is the numeric value 5.

If you apply ++ to a string, JavaScript coerces it into a number. In this case, "5" gets coerced to the number 5. After coercion, it then increments the value to 6. However, the return value is 5 since the post-increment operator (y++) returns the original value of y, not the incremented value.

This shows that x++ is not the same thing as x = x + 1.

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