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  • Ahmed Elgendy thinks this is interesting:

If you try to add a number and a string, JavaScript converts the number to a string and concatenates the two. Kind of the opposite of what it does with equality:

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If you put the string first and then use the + operator with a number, the same thing happens: the number is converted to a string and the two are joined by concatenation.

From

Cover of Head First JavaScript Programming

Note

What if you use + operator with two operands of two different types?