Another bit of JavaScript goodness you’ve come to rely on online is the mouseover effect—instances where hovering a mouse over a certain icon or area on a screen produces an action or result from the spot where you’re hovering. Mouseovers are a routine part of JavaScript development, so spending your time on a quick mouseover JavaScript project is a worthwhile way to spend the afternoon. Roger Van Hout’s Happy Bouncing Balls mouseover on CodePen displays a field of balls resembling the kind you’d get from gum machines as a kid. Hover your mouse over any single sphere and watch it expand.