input checked by default

    <form 
    action="/action_page.php">

   <input type="checkbox" name="vehicle1" value="Bike">
  <label 
    for="vehicle1"> I have a bike</label><br>
  <input type="checkbox" 
    name="vehicle2" value="Car">
  <label for="vehicle2"> I have a 
    car</label><br>
  <input type="checkbox" name="vehicle3" 
    value="Boat" checked>
  <label for="vehicle3"> I have a 
    boat</label><br><br>
  <input type="submit" value="Submit">

    </form>



#If if helps you give it Thumbs up 

   <input type="checkbox" checked={props.completed} /> 

#for props completed is true/false , hence if completed is false then checkbox will not be clicked .
# if the checkbox is true it will be will be checked

<input type="checkbox" checked>