Basic JavaScript Interview Questions and Answers

101 :: How to make a array as a stack using JavaScript?

The pop() and push() functions turn a harmless array into a stack in JavaScript...

<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

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102 :: 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 in JavaScript. Queues are easily implemented using combinations.

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103 :: 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 ""+myMovie.title+""");
<
This produces
movie: title "Aliens"
To create an object write a method with the name of 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]

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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104 :: How to associate functions with objects using JavaScript?

Now create a custom "toString()" method for our movie object. We can embed the function directly in the object like this.
<script type="text/javascript">
function movie(title, director) {
this.title = title;
this.director = director;
this.toString = function movieToString() {
return("title: "+this.title+" director: "+this.director);
}
}
var narnia = new movie("Narni","Andrew Adamson");
document.write(narnia.toString());
</script>
This produces
title: Narni director: Andrew Adamson
Or we can use a previously defined function and assign it to a variable. Note that the name of the function is not followed by parenthisis, otherwise it would just execute the function and stuff the returned value into the variable.
<script type="text/javascript">
function movieToString() {
return("title: "+this.title+" director: "+this.director);
}
function movie(title, director) {
this.title = title;
this.director = director;
this.toString = movieToString;
}
var aliens = new movie("Aliens","Cameron");
document.write(aliens.toString());
</script>
This produces
title: Aliens director: Cameron

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105 :: What is eval() in JavaScript?

The eval() method is incredibly powerful allowing us to execute snippets of code during execution in JavaScript.

<script type="text/javascript">
var USA_Texas_Austin = "521,289";
document.write("Population is "+eval("USA_"+"Texas_"+"Austin"));
</script>

This produces
Population is 521,289

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