How do I show a row in fields of the form?

I have a table which is generated from the database with PHP so I do not assign a id , the idea is to show the client records to assign them an address (with another form but I need the id of the client), I have functionality but reloading the page what I want is to do it with JavaScript and that simply when I give it in a link that is in the table (in the row of each client) that shows them in the fields of the forms without reload the page, but I have two days of learning it just do not know how to implement it. This is the html table already generated:

<table class="table table-bordered" id="tblClientes">
    <thead>
        <tr>
            <th>ID Cliente</th>
            <th>Cliente</th>
            <th>Documento</th>
        </tr>
    </thead>
    <tbody>
        <tr>            
            <td>1</td>
            <td>Cliente1 apellido1</td>
            <td>5467915414</td>
            <td>
                <center>
                    <a onclick="alertar(this)" class="waves-effect waves-dark" href="#" aria-expanded="false">
                        <i class="fa fa-edit" data-toggle="tooltip" title="" data-original-title="Seleccionar"></i>
                        <span class="hide-menu"></span>
                    </a>
                </center>
            </td>
        </tr>
        <tr>            
            <td>2</td>
            <td>Cliente2 apellido2</td>
            <td>5467915414</td>
            <td>
                <center>
                    <a onclick="alertar(this)" class="waves-effect waves-dark" href="#" aria-expanded="false">
                        <i class="fa fa-edit" data-toggle="tooltip" title="" data-original-title="Seleccionar"></i>
                        <span class="hide-menu"></span>
                    </a>
                </center>
            </td>
        </tr>
    </tbody>
</table>

And here I would send the data you select from the table (part of the form)

<div class="column">
    <label for="cliente">Cliente:</label>
    <input readonly style="width:88%;" type="text" class="form-control" id="cliente"  name="cliente">
</div>
    <div class="column">
        <label for="doc">Identificación:</label>
        <input readonly type="text" class="form-control" id="doc" name="doc">
</div>

This is javascript

function alertar(elemento){
    try{
        //trato de obtener el padre del a que seria el que llama a la funcion
        //pero me lo tira como undefined y entonces no puedo acceder al padre de este
        //del center para llegar hasta el <tr> para leer la fila
        var centerEl = elemento.parentNode;
        alert(centerEl.constructor);
    }catch(err){
        alert(err.message);
    }
    alert("Hola de prueba a la funcion");
}

What I try to do is to get to the <tr> with the <a> element that executes the function since there is no id (as the table comes from the base), I have a base of how to read the row of the table the problem would be that I do not get to get the row to do it since it tells me that it is undefined .