[Techmaker]

понятно, вот сравни и узнаешь:

n1u2=5
zn = "n1";
zu = "u2";
varName = zn+zu;
varValue = Number(varName) + 4
trace(varValue)

и

n1u2=5
zn = "n1";
zu = "u2";
varName = zn+zu;
varValue = this[varName] + 4
trace(varValue)

удачи