Unable to fetch element using document.getElementById

Question

<input class="form-check-input" type="radio" name="flexRadioDefault" id="flexRadioDefault3" >
<label class="form-check-label" for="flexRadioDefault3" id="label3">

i am trying to get the element by its id and print the same in console

var a = document.getElementById('flexRadioDefault3')
console.log(a)

the output in console should be

<input class="form-check-input" type="radio" name="flexRadioDefault" id="flexRadioDefault3" > 

but i am getting Null instead