Math.sign

Math.sign(x)

Math.sign(3);     //  1
Math.sign(-3);    // -1
Math.sign('-3');  // -1
Math.sign(0);     //  0
Math.sign(-0);    // -0
Math.sign(NaN);   // NaN
Math.sign('foo'); // NaN
Math.sign();      // NaN

if (!Math.sign) {
  Math.sign = function(x) {
    // If x is NaN, the result is NaN.
    // If x is -0, the result is -0.
    // If x is +0, the result is +0.
    // If x is negative and not -0, the result is -1.
    // If x is positive and not +0, the result is +1.
    return ((x > 0) - (x < 0)) || +x;
    // A more aesthetical persuado-representation is shown below
?   //
?   // ( (x > 0) ? 0 : 1 )  // if x is negative then negative one
?   //          +           // else (because you cant be both - and +)
?   // ( (x < 0) ? 0 : -1 ) // if x is positive then positive one
?   //         ||           // if x is 0, -0, or NaN, or not a number,
?   //         +x           // Then the result will be x, (or) if x is
?   //                      // not a number, then x converts to number
  };
}