(Math.floor(Math.random() * (20 - 10 + 1)) + 10) * (Math.random() < 0.5 ? -1 : 1)

function getRandom(min,max){ return Math.random()*(max-min)+min; }

Math.random() * (max - min) + min;

See details

Modification:

(Math.random() * (max - min) + min)*(Math.random()<0.5?1:-1);

function rand(min, max) { if ( min >= max ) { return; } return Math.floor(min + (max - min+1) * Math.random()); }

This is to take an integer within a range