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Javascript Interview Questions and Answers
How to Handle Event Handlers?
You can add an event handler in the HTML definition of the element like
this,
<script type="text/javascript"><!--
function hitme() {
alert("I've been hit!");
}
// -->
</script>
<input type="button" id="hitme" name="hitme" value="hit me" onclick="hitme()"
Or, interestingly enough you can just assign the event's name on the
object directly with a reference to the method you want to assign.
<input type="button" id="hitme2" name="hitme2" value="hit me2"/>
<script type="text/javascript"><!--
function hitme2() {
alert("I've been hit too!");
}
document.getElementById("hitme2").onclick = hitme2;
// -->
</script>
You can also use an anonymous method like this:
document.getElementById("hitme3").onclick = function () { alert("howdy!");
}
You can also use the W3C addEvventListener() method, but it does not
work in IE yet:
<input type="button" id="hitme4" name="hitme4" value="hit me4"/>
<script type="text/javascript"><!--
function hitme4() {
alert("I've been hit four!");
}
if(document.getElementById("hitme4").addEventListener) {
document.getElementById("hitme4").addEventListener("click", hitme4,
false);
}
// -->
</script>
How to remove the event listener:
?
<script type="text/javascript"><!--
document.getElementById("hitme4").removeEventListener("click", hitme4,
false);
// -->
</script>
Key Events
"onkeydown", "onkeypress", "onkeyup" events are supported both in ie and
standards-based browsers.
<script type="text/javascript">
function setStatus(name,evt) {
evt = (evt) ? evt : ((event) ? event : null); /* ie or standard? */
var charCode = evt.charCode;
var status = document.getElementById("keyteststatus");
var text = name +": "+evt.keyCode;
status.innerHTML = text;
status.textContent = text;
}
</script>
<form action="">
<input type="text" name="keytest" size="1" value=""
onkeyup="setStatus('keyup',event)"
onkeydown="setStatus('keydown',event)"
/>
<p id="keyteststatus">status</p>
</form>
How to make elements invisible ?
Change the "visibility" attribute of the style object associated with
your element. Remember that a hidden element still takes up space, use
"display" to make the space disappear as well.
if ( x == y) {
myElement.style.visibility = 'visible';
} else {
myElement.style.visibility = 'hidden';
}
How to set the cursor to wait ?
In theory, we should cache the current state of the cursor and then put
it back to its original state.
document.body.style.cursor = 'wait';
//do something interesting and time consuming
document.body.style.cursor = 'auto';
How to reload the current page ?
window.location.reload(true);
how to force a page to go to another page using JavaScript ?
<script language="JavaScript" type="text/javascript" ><!-- location.href="http://newhost/newpath/newfile.html";
//--></script>
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