JavaScript Adding Booleans

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It works like that because that’s how it’s specified to work.

EcmaScript standard specifies that unless either of the arguments is a string, the + operator is assumed to mean numeric addition and not string concatenation. Conversion to numeric values is explicitly mentioned:

Return the result of applying the addition operation to ToNumber( lprim) and ToNumber(rprim).

(where lprim and rprim are the primitive forms of the left-hand and the right-hand argument, respectively)

EcmaScript also specifies the To Number conversion for booleans clearly:

The result is 1 if the argument is true. The result is +0 if the argument is false.

Hence, true + true effectively means 1 + 1, or 2.

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