JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="checkbox" name="attr1" value="1" />
    <input type="checkbox" name="attr1" value="2" />
    <input type="checkbox" name="attr1" value="3" />
    <input type="checkbox" name="attr1" value="4" />
    <input type="checkbox" name="attr2" value="xx" />
    <input type="checkbox" name="attr3" value="a" />
    <input type="checkbox" name="attr3" value="b" />
    <input type="checkbox" name="attr3" value="c" />
    <input type="checkbox" name="attr3" value="d" />
    <input type="text" name="attr4" value="" />
</form>

JavaScript

var name_map = {};
$("input[type=checkbox]").each(function() {
    var name = this.name;
    name_map[name] = (name_map[name]) ? name + "[]" : name;
}).each(function() {
    this.name = name_map[this.name];
});