Implement these language features:
addition & subtraction
var a = 42; a + 1 + a - 42; // 43
multiplication & division
var a = 42; a * 1 / a * 42; // 42
postfix increment
var a = 42; a++ + 42; // 84 a; // 43
Of course, operator precedence should be handled correctly.
var a = 42; 500 - a++ * 10; // 80 a; // 43
Implement the other increment and decrement operators.
var x = 42; x++; // 42 ++x; // 44–x; // 43 x–; // 43 x; // 42
Implement the addition and subtraction assignment operators += and -=.
var x = 42; x += 10; // 52 x -= 50; // 2
Implement parenthesized subexpressions.
1 + 2 * 3; // 7 (1 + 2) * 3; // 9