Question

In the traditional way to add event listener:

function getComboA(sel) {
    var value = sel.options[sel.selectedIndex].value;  
}

<select id="comboA" onchange="getComboA(this)">
<option value="">Select combo</option>
<option value="Value1">Text1</option>
<option value="Value2">Text2</option>
<option value="Value3">Text3</option>
</select>

But I wanted to adapt to the addEventListener way:

productLineSelect.addEventListener('change',getSelection(this),false);

function getSelection(sel){
    var value = sel.options[sel.selectedIndex].value;
    alert(value);
}

It doesn’t work because I can’t pass any parameter in getSelection() as the second parameter in addEventListener method? As far as I know I can only use the function name without parenthesises.

Any idea?

BTW, please look at my previous question about console.log doesn’t work in Safari 6.0 Developer Inspector, I can’t write any output in the console, which is frustrating.

Answer 1

No need to pass anything in. The function used for addEventListener will automatically have this bound to the current element. Simply use this in your function:

productLineSelect.addEventListener('change', getSelection, false);

function getSelection() {
    var value = this.options[this.selectedIndex].value;
    alert(value);
}

Here’s the fiddle: http://jsfiddle.net/dJ4Wm/

---

If you want to pass arbitrary data to the function, wrap it in your own anonymous function call:

productLineSelect.addEventListener('change', function() {
    foo('bar');
}, false);

function foo(message) {
    alert(message);
}

Here’s the fiddle: http://jsfiddle.net/t4Gun/

---

If you want to set the value of this manually, you can use the call method to call the function:

var self = this;
productLineSelect.addEventListener('change', function() {
    getSelection.call(self);
    // This'll set the `this` value inside of `getSelection` to `self`
}, false);

function getSelection() {
    var value = this.options[this.selectedIndex].value;
    alert(value);
}