how can i change the value of checkbox when i select a value from select input with js

i want to learn that when i select a value from select input how can i change the value of checkbox.

<input type="checkbox" name="id" value="" id="mycheckbox1">

<select name="cat-1" id="myselectbox1">
    <option value="">Choose</option>      
    <option value="100">Value1</option>
    <option value="200">Value2</option>       
</select>