How to make a required field after activating a checkbox?

Question

JavaScript

Hello!
Help to implement the following functionality:
There is a form where it is necessary that after the active checkbox (click on it), the field in the form becomes mandatory.
I will be very grateful!

<TD CLASS="browseItemName" NOWRAP VALIGN="TOP">
<INPUT TYPE="CHECKBOX" ID="_1_1_4_[LL_REPTAG=ROWNUM /]_5_1" NAME="_1_1_4_[LL_REPTAG=ROWNUM /]_5_1" value="1"  ONCLICK="EditPosition('_1_1_4_[LL_REPTAG=ROWNUM /]_7_1', '_1_1_4_[LL_REPTAG=ROWNUM /]_5_1');markDirty();">
</TD>
<TD CLASS="browseItemName" NOWRAP VALIGN="TOP">
<TEXTAREA CLASS="valueEditable multiline rfield" ID="_1_1_4_[LL_REPTAG=ROWNUM /]_7_1" NAME="_1_1_4_[LL_REPTAG=ROWNUM /]_7_1" TITLE="Reason" WRAP="soft" ROWS="3" COLS="128" READONLY="TRUE" ONCHANGE="markDirty();"></TEXTAREA>
</TD>