var bg = document.getElementById('bb');
document.getElementById('gg').addEventListener("mouseover",
function(){bg.style.width = 50 + "%", bg.style.height = 50 + "%";
this.addEventListener("mouseout", function(){bg.style.width = "" , bg.style.height = "";});
});
var bh = document.getElementById('qq');
document.getElementById('gg').addEventListener("mouseover",
function(){bh.style.width = 50 + "%", bh.style.height = 50 + "%";
this.addEventListener("mouseout", function(){bh.style.width = "" , bh.style.height = "" ;});
});
var bj = document.getElementById('ee');
document.getElementById('gg').addEventListener("mouseover",
function(){bj.style.width = 50 + "%", bj.style.height = 50 + "%";
this.addEventListener("mouseout", function(){bj.style.width = "" , bj.style.height = "" ;});
});
var bk = document.getElementById('ww');
document.getElementById('gg').addEventListener("mouseover",
function(){bk.style.width = 50 + "%", bk.style.height = 50 + "%";
this.addEventListener("mouseout", function(){bk.style.width = "" , bk.style.height = "" ;});
});
добился желаемого эффекта созданием переменной на каждый изменяемый объект, с указанием id желаемой кнопки.