How are object properties assigned?
Assigning properties to objects is done in the same way as a value is assigned to a variable. For example, a form object’s action value is assigned as ‘submit’ in the following manner – Document.form.action=”submit”
What is the method for reading and writing a file in JavaScript?
This can be done by Using JavaScript extensions (runs from JavaScript Editor), example for opening of a file –
fh = fopen(getScriptPath(), 0);
How are DOM utilized in JavaScript?
DOM stands for Document Object Model and is responsible for how various objects in a document interact with each other. DOM is required for developing web pages, which includes objects like paragraph, links, etc. These objects can be operated to include actions like add or delete. DOM is also required to add extra capabilities to a web page. On top of that, the use of API gives an advantage over other existing models.
How are event handlers utilized in JavaScript?
Events are the actions that result from activities, such as clicking a link or filling a form, by the user. An event handler is required to manage proper execution of all these events. Event handlers are an extra attribute of the object. This attribute includes event’s name and the action taken if the event takes place.
Explain the role of deferred scripts in JavaScript?
By default, the parsing of the HTML code, during page loading, is paused until the script has not stopped executing. It means, if the server is slow or the script is particularly heavy, then the webpage is displayed with a delay. While using Deferred, scripts delays execution of the script till the time HTML parser is running. This reduces the loading time of web pages and they get displayed faster.
What are the various functional components in JavaScript?
The different functional components in JavaScript are-
First-class functions: Functions in JavaScript are utilized as first class objects. This usually means that these functions can be passed as arguments to other functions, returned as values from other functions, assigned to variables or can also be stored in data structures.
Nested functions: The functions, which are defined inside other functions, are called Nested functions. They are called ‘everytime’ the main function is invoked.
Write about the errors shown in JavaScript?
JavaScript gives a message if it encounters an error. The recognized errors are –
Load-time errors: The errors shown at the time of the page loading are counted under Load-time errors. These errors are encountered by the use of improper syntax, and thus are detected while the page is getting loaded.
Run-time errors: This is the error that comes up while the program is running. It is caused by illegal operations, for example, division of a number by zero, or trying to access a non-existent area of the memory.
Logic errors: It is caused by the use of syntactically correct code, which does not fulfill the required task. For example, an infinite loop.
What are Screen objects?
Screen objects are used to read the information from the client’s screen. The properties of screen objects are –
AvalHeight: Gives the height of client’s screen
AvailWidth: Gives the width of client’s screen.
ColorDepth: Gives the bit depth of images on the client’s screen
Height: Gives the total height of the client’s screen, including the taskbar
Width: Gives the total width of the client’s screen, including the taskbar
Explain the unshift() method ?
This method is functional at the starting of the array, unlike the push(). It adds the desired number of elements to the top of an array. For example –
var name = [ "john" ];
name.unshift( "charlie" );
name.unshift( "joseph", "Jane" );
console.log(name);
The output is shown below:
[" Jane ", " joseph ", " charlie ", " john "]
Define unescape() and escape() functions?
The escape () function is responsible for coding a string so as to make the transfer of the information from one computer to the other, across a network.
For Example:
<script>
document.write(escape(“Hello? How are you!”));
</script>
Output: Hello%3F%20How%20are%20you%21
The unescape() function is very important as it decodes the coded string.
It works in the following way. For example:
<script>
document.write(unescape(“Hello%3F%20How%20are%20you%21”));
</script>
Output: Hello? How are you!
What are the decodeURI() and encodeURI()?
EncodeURl() is used to convert URL into their hex coding. And DecodeURI() is used to convert the encoded URL back to normal.
<script>
var uri="my test.asp?name=ståle&car=saab";
document.write(encodeURI(uri)+ "<br>");
document.write(decodeURI(uri));
</script>
Output –
my%20test.asp?name=st%C3%A5le&car=saab
my test.asp?name=ståle&car=saab
Why it is not advised to use innerHTML in JavaScript?
innerHTML content is refreshed every time and thus is slower. There is no scope for validation in innerHTML and, therefore, it is easier to insert rouge code in the document and, thus, make the web page unstable.
What does the following statement declares?
var myArray = [[[]]];
It declares a three dimensional array.
How are JavaScript and ECMA Script related?
ECMAScript is nothing but another name for JavaScript. Precisely, ECMAScript is the formal name of JavaScript, when XML elements have to be accessed.
What is namespacing in JavaScript and how is it used?
Namespacing is used for grouping the desired functions, variables etc. under a unique name. It is a name that has been attached to the desired functions, objects and properties. This improves modularity in the coding and enables code reuse.
How can JavaScript codes be hidden from old browsers that don’t support JavaScript?
For hiding JavaScript codes from old browsers:
Add “<!–” without the quotes in the code just after the <script> tag.
Add “//–>” without the quotes in the code just before the <script> tag.
Old browsers will now treat this JavaScript code as a long HTML comment. While, a browser that supports JavaScript, will take the “<!–” and “//–>” as one-line comments.
What is a potential pitfall with using typeof bar === "object" to determine if bar is an object? How can this pitfall be avoided?
Although typeof bar === "object" is a reliable way of checking if bar is an object, the surprising gotcha in JavaScript is that null is also considered an object!
Therefore, the following code will, to the surprise of most developers, log true (not false) to the console:
var bar = null;
console.log(typeof bar === "object"); // logs true!
As long as one is aware of this, the problem can easily be avoided by also checking if bar is null:
console.log((bar !== null) && (typeof bar === "object")); // logs false
To be entirely thorough in our answer, there are two other things worth noting:
First, the above solution will return false if bar is a function. In most cases, this is the desired behavior, but in situations where you want to also return true for functions, you could amend the above solution to be:
console.log((bar !== null) && ((typeof bar === "object") || (typeof bar === "function")));
Second, the above solution will return true if bar is an array (e.g., if var bar = [];). In most cases, this is the desired behavior, since arrays are indeed objects, but in situations where you want to also false for arrays, you could amend the above solution to be:
console.log((bar !== null) && (typeof bar === "object") && (toString.call(bar) !== "[object Array]"));
However, there’s one other alternative that returns false for nulls, arrays, and functions, but true for objects:
console.log((bar !== null) && (bar.constructor === Object));
Or, if you’re using jQuery:
console.log((bar !== null) && (typeof bar === "object") && (! $.isArray(bar)));
ES5 makes the array case quite simple, including its own null check:
console.log(Array.isArray(bar));
What will the code below output to the console and why?
(function(){
var a = b = 3;
})();
console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));
Since both a and b are defined within the enclosing scope of the function, and since the line they are on begins with the var keyword, most JavaScript developers would expect typeof a and typeof b to both be undefined in the above example.
However, that is not the case. The issue here is that most developers incorrectly understand the statement var a = b = 3; to be shorthand for:
var b = 3;
var a = b;
But in fact, var a = b = 3; is actually shorthand for:
b = 3;
var a = b;
As a result (if you are not using strict mode), the output of the code snippet would be:
a defined? false
b defined? true
But how can b be defined outside of the scope of the enclosing function? Well, since the statement var a = b = 3; is shorthand for the statements b = 3; and var a = b;, b ends up being a global variable (since it is not preceded by the var keyword) and is therefore still in scope even outside of the enclosing function.
Note that, in strict mode (i.e., with use strict), the statement var a = b = 3; will generate a runtime error of ReferenceError: b is not defined, thereby avoiding any headfakes/bugs that might othewise result. (Yet another prime example of why you should use use strict as a matter of course in your code!).
Assigning properties to objects is done in the same way as a value is assigned to a variable. For example, a form object’s action value is assigned as ‘submit’ in the following manner – Document.form.action=”submit”
What is the method for reading and writing a file in JavaScript?
This can be done by Using JavaScript extensions (runs from JavaScript Editor), example for opening of a file –
fh = fopen(getScriptPath(), 0);
How are DOM utilized in JavaScript?
DOM stands for Document Object Model and is responsible for how various objects in a document interact with each other. DOM is required for developing web pages, which includes objects like paragraph, links, etc. These objects can be operated to include actions like add or delete. DOM is also required to add extra capabilities to a web page. On top of that, the use of API gives an advantage over other existing models.
How are event handlers utilized in JavaScript?
Events are the actions that result from activities, such as clicking a link or filling a form, by the user. An event handler is required to manage proper execution of all these events. Event handlers are an extra attribute of the object. This attribute includes event’s name and the action taken if the event takes place.
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| Adobe Systems Most Frequently Asked Latest JavaScript Interview Questions Answers |
Explain the role of deferred scripts in JavaScript?
By default, the parsing of the HTML code, during page loading, is paused until the script has not stopped executing. It means, if the server is slow or the script is particularly heavy, then the webpage is displayed with a delay. While using Deferred, scripts delays execution of the script till the time HTML parser is running. This reduces the loading time of web pages and they get displayed faster.
What are the various functional components in JavaScript?
The different functional components in JavaScript are-
First-class functions: Functions in JavaScript are utilized as first class objects. This usually means that these functions can be passed as arguments to other functions, returned as values from other functions, assigned to variables or can also be stored in data structures.
Nested functions: The functions, which are defined inside other functions, are called Nested functions. They are called ‘everytime’ the main function is invoked.
Write about the errors shown in JavaScript?
JavaScript gives a message if it encounters an error. The recognized errors are –
Load-time errors: The errors shown at the time of the page loading are counted under Load-time errors. These errors are encountered by the use of improper syntax, and thus are detected while the page is getting loaded.
Run-time errors: This is the error that comes up while the program is running. It is caused by illegal operations, for example, division of a number by zero, or trying to access a non-existent area of the memory.
Logic errors: It is caused by the use of syntactically correct code, which does not fulfill the required task. For example, an infinite loop.
What are Screen objects?
Screen objects are used to read the information from the client’s screen. The properties of screen objects are –
AvalHeight: Gives the height of client’s screen
AvailWidth: Gives the width of client’s screen.
ColorDepth: Gives the bit depth of images on the client’s screen
Height: Gives the total height of the client’s screen, including the taskbar
Width: Gives the total width of the client’s screen, including the taskbar
Explain the unshift() method ?
This method is functional at the starting of the array, unlike the push(). It adds the desired number of elements to the top of an array. For example –
var name = [ "john" ];
name.unshift( "charlie" );
name.unshift( "joseph", "Jane" );
console.log(name);
The output is shown below:
[" Jane ", " joseph ", " charlie ", " john "]
Define unescape() and escape() functions?
The escape () function is responsible for coding a string so as to make the transfer of the information from one computer to the other, across a network.
For Example:
<script>
document.write(escape(“Hello? How are you!”));
</script>
Output: Hello%3F%20How%20are%20you%21
The unescape() function is very important as it decodes the coded string.
It works in the following way. For example:
<script>
document.write(unescape(“Hello%3F%20How%20are%20you%21”));
</script>
Output: Hello? How are you!
What are the decodeURI() and encodeURI()?
EncodeURl() is used to convert URL into their hex coding. And DecodeURI() is used to convert the encoded URL back to normal.
<script>
var uri="my test.asp?name=ståle&car=saab";
document.write(encodeURI(uri)+ "<br>");
document.write(decodeURI(uri));
</script>
Output –
my%20test.asp?name=st%C3%A5le&car=saab
my test.asp?name=ståle&car=saab
Why it is not advised to use innerHTML in JavaScript?
innerHTML content is refreshed every time and thus is slower. There is no scope for validation in innerHTML and, therefore, it is easier to insert rouge code in the document and, thus, make the web page unstable.
What does the following statement declares?
var myArray = [[[]]];
It declares a three dimensional array.
How are JavaScript and ECMA Script related?
ECMAScript is nothing but another name for JavaScript. Precisely, ECMAScript is the formal name of JavaScript, when XML elements have to be accessed.
What is namespacing in JavaScript and how is it used?
Namespacing is used for grouping the desired functions, variables etc. under a unique name. It is a name that has been attached to the desired functions, objects and properties. This improves modularity in the coding and enables code reuse.
How can JavaScript codes be hidden from old browsers that don’t support JavaScript?
For hiding JavaScript codes from old browsers:
Add “<!–” without the quotes in the code just after the <script> tag.
Add “//–>” without the quotes in the code just before the <script> tag.
Old browsers will now treat this JavaScript code as a long HTML comment. While, a browser that supports JavaScript, will take the “<!–” and “//–>” as one-line comments.
What is a potential pitfall with using typeof bar === "object" to determine if bar is an object? How can this pitfall be avoided?
Although typeof bar === "object" is a reliable way of checking if bar is an object, the surprising gotcha in JavaScript is that null is also considered an object!
Therefore, the following code will, to the surprise of most developers, log true (not false) to the console:
var bar = null;
console.log(typeof bar === "object"); // logs true!
As long as one is aware of this, the problem can easily be avoided by also checking if bar is null:
console.log((bar !== null) && (typeof bar === "object")); // logs false
To be entirely thorough in our answer, there are two other things worth noting:
First, the above solution will return false if bar is a function. In most cases, this is the desired behavior, but in situations where you want to also return true for functions, you could amend the above solution to be:
console.log((bar !== null) && ((typeof bar === "object") || (typeof bar === "function")));
Second, the above solution will return true if bar is an array (e.g., if var bar = [];). In most cases, this is the desired behavior, since arrays are indeed objects, but in situations where you want to also false for arrays, you could amend the above solution to be:
console.log((bar !== null) && (typeof bar === "object") && (toString.call(bar) !== "[object Array]"));
However, there’s one other alternative that returns false for nulls, arrays, and functions, but true for objects:
console.log((bar !== null) && (bar.constructor === Object));
Or, if you’re using jQuery:
console.log((bar !== null) && (typeof bar === "object") && (! $.isArray(bar)));
ES5 makes the array case quite simple, including its own null check:
console.log(Array.isArray(bar));
What will the code below output to the console and why?
(function(){
var a = b = 3;
})();
console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));
Since both a and b are defined within the enclosing scope of the function, and since the line they are on begins with the var keyword, most JavaScript developers would expect typeof a and typeof b to both be undefined in the above example.
However, that is not the case. The issue here is that most developers incorrectly understand the statement var a = b = 3; to be shorthand for:
var b = 3;
var a = b;
But in fact, var a = b = 3; is actually shorthand for:
b = 3;
var a = b;
As a result (if you are not using strict mode), the output of the code snippet would be:
a defined? false
b defined? true
But how can b be defined outside of the scope of the enclosing function? Well, since the statement var a = b = 3; is shorthand for the statements b = 3; and var a = b;, b ends up being a global variable (since it is not preceded by the var keyword) and is therefore still in scope even outside of the enclosing function.
Note that, in strict mode (i.e., with use strict), the statement var a = b = 3; will generate a runtime error of ReferenceError: b is not defined, thereby avoiding any headfakes/bugs that might othewise result. (Yet another prime example of why you should use use strict as a matter of course in your code!).