Question

want to make values of the oject’s dynamic (from user input) but I get “undefined”. The idea is to have 3 input fields and the user should input values in them which will fill up the alert message.

<script type="text/javascript">
function Family (fatherName, motherName, sisterName) {

    this.fatherName = fatherName;
    this.motherName = motherName;
    this.sisterName = sisterName;
    this.myFamily = function() {
        alert("My father's name is " + this.fatherName +", my mother's name is "+ this.motherName +" and my sister's name is " + this.sisterName +".");
    }

}

var Me = new Family(
    Family["fatherName"] = father,
    Family["motherName"] = mother,
    Family["sisterName"] = siter);

var father = document.getElementById("fatherId").value;
var mother = document.getElementById("motherId").value;
var sister = document.getElementById("sisterId").value;
</script>

<input type="text" id="fatherId" />
<input type="text" id="motherId" />
<input type="text" id="fatherId" />
<input type="submit" value="Send" onclick="Me.myFamily();"> 

Also I’m looking for a way how user can add or remove properties (values in them, too).

Answer 1

Here is the working snippet of your example.

<input type="text" id="fatherId" />
<input type="text" id="motherId" />
<input type="text" id="sisterId" />
<input type="submit" value="Send" id="submit" />

<script>
    function Family(fatherName, motherName, sisterName) {

      this.fatherName = fatherName;
      this.motherName = motherName;
      this.sisterName = sisterName;

      this.myFamily = function() {
          alert("My father's name is " + this.fatherName + 
                ", my mother's name is " + this.motherName + 
                " and my sister's name is " + this.sisterName + ".");
      };

    }

    document.getElementById("submit").onclick = function() {
        var father = document.getElementById("fatherId").value;
        var mother = document.getElementById("motherId").value;
        var sister = document.getElementById("sisterId").value;

        Me = new Family(father, mother, sister);
        Me.myFamily();
    }
</script>

All the mistakes are summarized very well by Brandon.

*EDIT: (anser to your comment)

Your code has two execution related problems.

• <script> tags are executed immediately and therefore if you insert script before the <input> part then there are no input elements available for you to retrieve.
• You want to retrieve values of the inputs, but those inputs contain data when user clicks on the submit and therefore must be read using .value() at the onclick time. If you try to read them outside the onclick part then they are accessed immediately during page load when the input fields are empty.