for (let i = 0; i < contact.length; i++) {

  contact[i].addEventListener("click", function() {

    if (i === 0) {

      console.log(i);

      firstnameFunc();

    } else if (i === 1) {

      lastnameFunc();

      console.log(i);

    } else if (i === 2) {

      emailFunc();

      console.log(i);

    } else if (i === 3) {

      phoneFunc();

      console.log(i);

    } else if (i === 4) {

      genderFunc();

      console.log(i);

    } else if (i === 5) {

      interestFunc();

      console.log(i);

    } else if (i === 6) {

      messageFunc();

      console.log(i);

    }

  });

}

​

function firstnameFunc() {

  contact[0].className = "selected";

  contact[1].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[3].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function lastnameFunc() {

  contact[1].className = "selected";

  contact[0].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[3].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function emailFunc() {

  contact[2].className = "selected";

  contact[1].className = "nonSelected";

  contact[0].className = "nonSelected";

  contact[3].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function phoneFunc() {

  contact[3].className = "selected";

  contact[1].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[0].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function genderFunc() {

  contact[4].className = "selected";

  contact[0].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[3].className = "nonSelected";

  contact[1].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function interestFunc() {

  contact[5].className = "selected";

  contact[1].className = "nonSelected";

  contact[0].className = "nonSelected";

  contact[3].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[6].className = "nonSelected";

}

function messageFunc() {

  contact[6].className = "selected";

  contact[1].className = "nonSelected";

  contact[2].className = "nonSelected";

  contact[0].className = "nonSelected";

  contact[4].className = "nonSelected";

  contact[5].className = "nonSelected";

  contact[3].className = "nonSelected";

}