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Javascript Interview Questions and Answers
How to Accessing Elements using
javascript?
To do something interesting with HTML elements, we must first be able to
uniquely identify which element we want. In the example
<body>
<form action="">
<input type="button" id="useless" name="mybutton" value="doNothing" />
</form>
</body>
We can use the "getElementById" method (which is generally preferred)
document.getElementById("useless").style.color = "red";
or we can use the older hierarchical navigation method,
document.forms[0].mybutton.style.color = "blue";
Notice that this uses the "name" attribute of the element to locate it.
# Example of Accessing Elements in a DOM.
<script type="text/javascript" >
function showStatus() {
var selectWidget = document.forms.beerForm.elements["beer"];
var myValue = selectWidget.options[selectWidget.selectedIndex].value;
alert('You drank a \"'+ myValue +"\"");
return true;
}
</script>
<form name="beerForm" action="">
<select name="beer">
<option selected="selected">Select Beer</option>
<option>Heineken</option>
<option>Amstel Light</option>
<option>Corona</option>
<option>Corona Light</option>
<option>Tecate</option>
</select>
<input type="button" name="submitbutton" value="Drink"
onclick="showStatus()" />
</form>
What looping structures are there in JavaScript?
for, while, do-while loops, but no foreach.
To put a "close window" link on a page ?
<a href='javascript:window.close()' class='mainnav'> Close </a>
How to hide javascript code from old browsers that dont run it?
Use the below specified style of comments <script language=javascript>
<!-- javascript code goes here // --> or Use the <NOSCRIPT>some html
code </NOSCRIPT> tags and code the display html statements between these
and this will appear on the page if the browser does not support
javascript
How to comment javascript code?
Use // for line comments and
/*
*/ for block comments
Name the numeric constants representing max,min values
Number.MAX_VALUE
Number.MIN_VALUE
What does javascript null mean?
The null value is a unique value representing no value or no object.
It implies no object,or null string,no valid boolean value,no number and
no array object.
How do you create a new object in JavaScript?
var obj = new Object(); or var obj = {};
How do you assign object properties?
obj["age"] = 17 or obj.age = 17.
What’s a way to append a value to an array?
arr[arr.length] = value;
What is this keyword?
It refers to the current object.
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