Ed/Ex is text editor, old text editor on that day didn’t have WYSIWYG text editor,
You need to use ed syntax to edit your text file.
If you know sed, It is stream ed.
Vim is based on ed, Example substitue synax :s/old/new is come form ed syntax.
You should learn ed to empower your vim skill.
# Input
var path = require('path');
var mongo = require('mongo');
var express = require('express');
var x = 2;
var y = 3;
var z = 4;
want to change var to const only in line that contain require
find line that has < contain word > then replace < word > to < new word > on that line
:g/< contain word >/s/< word >/ < new word >/g
# vim command
:g/require/s/var/const/g
# Output
const path = require('path');
const mongo = require('mongo');
const express = require('express');
var x = 2;
var y = 3;
var z = 4;
find line that not has < contain word > then replace < word > to < new word > on that line
:v/< contain word >/s/< word >/ < new word >/g
# Vim command
:v/require/s/var/let/g
# Output
var path = require('path');
var mongo = require('mongo');
var express = require('express');
let x = 2;
let y = 3;
let z = 4;