What does console.log(1 + '2' - 1) output?

Console output

Why

+ and - have the same precedence and are left-associative, so this is (1 + "2") - 1. The + sees a string and concatenates: 1 + "2" is "12". Then "12" - 1 uses numeric coercion because - has no string meaning, giving 12 - 1 = 11. The asymmetry between + and - flips the value mid-expression.