js method to get the element of class and create method getElementsByClassName

function getElementsByClassName(n) {
var classElements = [],allElements = ('*');
for (var i=0; i< ; i++ )
{
if (allElements[i].className == n ) {
classElements[] = allElements[i];
}
}
return classElements;
}

var redClassElements = getElementsByClassName('aa');
for (var i=0; i<; i++) {
      //do something
}