Question

I am new to Javascript. I have set a couple of buttons on a page, like this:

<div id='MID_1_4'>
    <div id="login">logout</div>
    <button type="button" id="logout" onclick="loadXMLDoc2()">Logout</button>
</div>
...

I want to extract the id of the button who called loadXMLDoc2(). This method is defined as following:

function loadXMLDoc2() {

    var retr = $(this).attr("id");
    document.getElementById("L1_LEFT").innerHTML
        = retr;

}

Yet, L1_LEFT is set to undefined when I click on buttons. I thought $(this) meant “the current HTML element”. If it is not the button then what is it? And how can I extract the button’s id?

Answer 1

this refers to window (the global object) inside the function, this refers to the element in the onclick handler.

while it’s bad approach to do javascript in html, try this:

<div id='MID_1_4'>
    <div id="login">logout</div>
    <button type="button" id="logout" onclick="loadXMLDoc2(this)">Logout</button>
</div>

function loadXMLDoc2(elm) {

    var retr = elm.id;
    document.getElementById("L1_LEFT").innerHTML
    = retr;

}

A better approach is to separate HTML and javascript:

<div id='MID_1_4'>
    <div id="login">logout</div>
    <button type="button" id="logout">Logout</button>
</div>

(Somewhere in js file )

function loadXMLDoc2(elm) {

    var retr = elm.id;
    document.getElementById("L1_LEFT").innerHTML = retr;

}

$( document ).ready( function(){
//This function is executed after all elements on the page are ready to be manipulated

    $( "#logout" ).bind( "click",
        function(){
        loadXMLDoc2( this );
        }
    );
});