JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="text" name="nm1[]" value="a"/><input type="text" name="nm2[]" value="b"/>
    <input type="text" name="nm1[]" value="c"/><input type="text" name="nm2[]" value="d"/>
</form>

JavaScript

var nm1 = document.getElementsByName('nm1[]'),
    nm2 = document.getElementsByName('nm2[]'),
    i, o = {
        employees: []
    };
for (i = 0; i < nm1.length; ++i) {
    if (nm1[i].value && nm2[i].value)
        o.employees.push({
            firstName: nm1[i].value,
            lastName: nm2[i].value
        });
}
console.log(JSON.stringify(o));