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Javascript Interview Questions and Answers



How to use strings as array indexes using JavaScript?
Javascript does not have a true hashtable object, but through its wierdness, you can use the array as a hashtable.

<script type="text/javascript">
var days = ["Sunday","Monday","Tuesday","Wednesday", "Thursday","Friday","Saturday"];

for(var i=0; i < days.length; i++) {
days[days[i]] = days[i];
}

document.write("days[\"Monday\"]:"+days["Monday"]);
</script>
This produces
days["Monday"]:Monday

How to use "join()" to create a string from an array using JavaScript?
"join" concatenates the array elements with a specified seperator between them.

<script type="text/javascript">
var days = ["Sunday","Monday","Tuesday","Wednesday", "Thursday","Friday","Saturday"];
document.write("days:"+days.join(","));
</script>
This produces
days:Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday

How to make a array as a stack using JavaScript?
The pop() and push() functions turn a harmless array into a stack

<script type="text/javascript">
var numbers = ["one", "two", "three", "four"];
numbers.push("five");
numbers.push("six");
document.write(numbers.pop());
document.write(numbers.pop());
document.write(numbers.pop());
</script>
This produces
sixfivefour

How to shift and unshift using JavaScript?
<script type="text/javascript">
var numbers = ["one", "two", "three", "four"];
numbers.unshift("zero");
document.write(" "+numbers.shift());
document.write(" "+numbers.shift());
document.write(" "+numbers.shift());
</script>
This produces
zero one two
shift, unshift, push, and pop may be used on the same array. Queues are easily implemented using combinations.

How to create an object using JavaScript?
Objects can be created in many ways. One way is to create the object and add the fields directly.

<script type="text/javascript">
var myMovie = new Object();
myMovie.title = "Aliens";
myMovie.director = "James Cameron";
document.write("movie: title is \""+myMovie.title+"\"");
<
This produces
movie: title is "Aliens"
To create an object you write a method with the name of your object and invoke the method with "new".
<script type="text/javascript">
function movie(title, director) {
this.title = title;
this.director = director;
}
var aliens = new movie("Aliens","Cameron");
document.write("aliens:"+aliens.toString());
</script>
This produces
aliens:[object Object]

You can also use an abbreviated format for creating fields using a ":" to separate the name of the field from its value. This is equivalent to the above code using "this.".
<script type="text/javascript">
function movie(title, director) {
title : title;
director : director;
}
var aliens = new movie("Aliens","Cameron");
document.write("aliens:"+aliens.toString());
</script>
This produces
aliens:[object Object]
 

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