Remember folks, parseInt() is not eval().
parseInt("1", 10); // 1
eval("1") // 1
Pretty much the same thing....wait.
parseInt("1 + 1", 10); // 1
eval("1 + 1") // 2
In the first example the first digit is recognized and the rest of the string is thrown away. How intuitive. eval() at least gets it right.
parseInt("1 - 1", 10); // 1
eval("1 - 1") // 0
The string example takes the first digit and just throws out the rest of the string. And again, eval() with the correct solution.
parseInt("1" + "1", 10) // 11
eval("1" + "1") // 11
This time they both get the wrong answer, because the strings are concatenated before the numbers are evaluated.
parseInt("1" - "1", 10); // 0
eval ("1" - "1") // 0
Both right answers, because the subtraction symbol forces the strings into numbers before they get used.
-- @xjamundx