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Javascript Interview Questions and Answers



How to associate functions with objects using JavaScript?
Let's 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 parenthesis, 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; //assign function to this method pointer
}
var aliens = new movie("Aliens","Cameron");
document.write(aliens.toString());
</script>
This produces
title: Aliens director: Cameron

eval()?
The eval() method is incredibly powerful allowing you to execute snippets of code during execution.
<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

What does break and continue statements do?
Continue statement continues the current loop (if label not specified) in a new iteration whereas break statement exits the current loop.

How to create a function using function constructor?
The following example illustrates this
It creates a function called square with argument x and returns x multiplied by itself.
var square = new Function ("x","return x*x");

What's Prototypes for JavaScript?
Objects have "prototypes" from which they may inherit fields and functions.
<script type="text/javascript">
function movieToString() {
return("title: "+this.title+" director: "+this.director);
}
function movie(title, director) {
this.title = title;
this.director = director || "unknown"; //if null assign to "unknown"
this.toString = movieToString; //assign function to this method pointer
}
movie.prototype.isComedy = false; //add a field to the movie's prototype
var officeSpace = new movie("OfficeSpace");
var narnia = new movie("Narni","Andrew Adamson");
document.write(narnia.toString());
document.write("
Narnia a comedy? "+narnia.isComedy);
officeSpace.isComedy = true; //override the default just for this object
document.write("
Office Space a comedy? "+officeSpace.isComedy);
</script>

unescape(), escape()
These are similar to the decodeURI() and encodeURI(), but escape() is used for only portions of a URI.

<script type="text/javascript">
var myvalue = "Sir Walter Scott";
document.write("Original myvalue: "+myvalue);
document.write("<br />escaped: "+escape(myvalue));
document.write("<br />uri part: \"&author="+escape(myvalue)+"\"");
</script>

If you use escape() for the whole URI... well bad things happen.
<script type="text/javascript">
var uri = "http://www.google.com/search?q=sonofusion Taleyarkhan"
document.write("Original uri: "+uri);
document.write("
escaped: "+escape(uri));
v/script>

decodeURI(), encodeURI()
Many characters cannot be sent in a URL, but must be converted to their hex encoding. These functions are used to convert an entire URI (a superset of URL) to and from a format that can be sent via a URI.
<script type="text/javascript">
var uri = "http://www.google.com/search?q=sonofusion Taleyarkhan"
document.write("Original uri: "+uri);
document.write("<br />encoded: "+encodeURI(uri));
</script>

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