Why does + + treat a string as a number

Question

If you execute the following statement

"Test a b " + "c"
// Output
// "Test a b c"

but if you execute the following it treats "c" as a number.

"Test a b " + + "c"
// Output
// "Test a b NaN"

Why does two consecutive + signs treat the string as a number?

Tested in chrome 40.0.2214.111 m

see http://stackoverflow.com/questions/9549780/what-does-this-symbol-mean-in-javascript — Stuart, Feb 19 '15 at 02:20

score 8 · Answer 1 · answered Feb 19 '15 at 02:16

8

When you do "Test a b " + + "c", it is doing ("Test a b ") + (+ "c"), the first + is the string concatenation operator and the second + is the unary + operator, which converts to a Number

answered Feb 19 '15 at 02:16

Paul S.

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Interesting, thanks. I've learnt something new, I can use the unary + operator to cast to a number. – Ally Feb 19 '15 at 02:27

Why does + + treat a string as a number

1 Answers1