How to match and do some

Neovim
1

in a project
have text
a.js

function aaa (){ }
function bbb (){ }

b.vue

<div> aaa </dev>
<div> bbb </dev>
<!-- aaa  -->
<!-- bbb  -->

Q1: how to do replace part of aaa to ccc
turn to
a.js

function ccc (){ }
function bbb (){ }

b.vue

<div> ccc </dev>
<div> bbb </dev>
<!-- aaa  -->
<!-- bbb  -->

Q2: how to do comment includes aaa line
turn to
a.js

// function aaa (){ }
function bbb (){ }

b.vue

<!--<div> aaa </dev>-->
<div> bbb </dev>
<!-- aaa  -->
<!-- bbb  -->

Q3: how to do delete includes aaa line
turn to
a.js


function bbb (){ }

b.vue


<div> bbb </dev>

<!-- bbb  -->