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isNan function returns true if the argument is not a number otherwise it is false.
6. What is negative infinity?
Breaking within a string statement can be done by the use of a backslash, ‘\’, at the end of the first line
9. What are undeclared and undefined variables?
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.
Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.
10. Write the code for adding new elements dynamically?
Global variables are those that are available throughout the length of the code, that is, these have no scope. The var keyword is used to declare a local variable or object. If the var keyword is omitted, a global variable is declared.
// Declare a global globalVariable = “Test”;
The problems that are faced by using global variables are the clash of variable names of local and global scope. Also, it is difficult to debug and test the code that relies on global variables.
12. What is a prompt box?
A prompt box is a box which allows the user to enter input by providing a text box. Label and box will be provided to enter the text or number.
‘This’ keyword refers to the object from where it was called.
Timers are used to execute a piece of code at a set time or also to repeat the code in a given interval of time. This is done by using the functions setTimeout, setInterval and clearInterval.
The setTimeout(function, delay) function is used to start a timer that calls a particular function after the mentioned delay. The setInterval(function, delay) function is used to repeatedly execute the given function in the mentioned delay and only halts when cancelled. The clearInterval(id) function instructs the timer to stop.
Timers are operated within a single thread, and thus events might queue up, waiting to be executed.
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16. What is the difference between ViewState and SessionState?
‘ViewState’ is specific to a page in a session.
‘SessionState’ is specific to user specific data that can be accessed across all pages in the web application.
17. What is === operator?
=== is called as strict equality operator which returns true when the two operands are having the same value without any type conversion.
20. How can the style/class of an element be changed?
It can be done in the following way:
- Using a web page and Active X objects
- do-while loops
Variable typing is used to assign a number to a variable and the same variable can be assigned to a string.
The parseInt() function is used to convert numbers between different bases. parseInt() takes the string to be converted as its first parameter, and the second parameter is the base of the given string.
In order to convert 4F (of base 16) to integer, the code used will be –
“==” checks only for equality in value whereas “===” is a stricter equality test and returns false if either the value or the type of the two variables are different.
26. What would be the result of 3+2+”7″?
Since 3 and 2 are integers, they will be added numerically. And since 7 is a string, its concatenation will be done. So the result would be 57.
27. Explain how to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.platform string (property) should be used.
The NULL value is used to represent no value or no object. It implies no object or null string, no valid boolean value, no number and no array object.
29. What is the function of delete operator?
The functionality of delete operator is used to delete all variables and objects in a program but it cannot delete variables declared with VAR keyword.
Undefined value means the
- Variable used in the code doesn’t exist
- Variable is not assigned to any value
- Property doesn’t exist
- Confirm and
Void(0) is used to prevent the page from refreshing and parameter “zero” is passed while calling.
Void(0) is used to call another method without refreshing the page.
The following code has to be inserted to achieve the desired effect:
35. What is the difference between an alert box and a confirmation box?
An alert box displays only one button which is the OK button.
But a Confirmation box displays two buttons namely OK and cancel.
36. What are escape characters?
Escape characters (Backslash) is used when working with special characters like single quotes, double quotes, apostrophes and ampersands. Place backslash before the characters to make it display.
Cookies are the small test files stored in a computer and it gets created when the user visits the websites to store information that they need. Example could be User Name details and shopping cart information from the previous visits.
The pop() method is similar as the shift() method but the difference is that the Shift method works at the start of the array. Also the pop() method take the last element off of the given array and returns it. The array on which is called is then altered.
var cloths = [“Shirt”, “Pant”, “TShirt”];
//Now cloth becomes Shirt,Pant
- Content is replaced everywhere
- We cannot use like “appending to innerHTML”
- Even if you use +=like “innerHTML = innerHTML + ‘html’” still the old content is replaced by html
- The entire innerHTML content is re-parsed and build into elements, therefore its much slower
- The innerHTML does not provide validation and therefore we can potentially insert valid and broken HTML in the document and break it
Break statement exits from the current loop.
Continue statement continues with next statement of the loop.
They are as –
- Reference types.
43. How generic objects can be created?
Generic objects can be created as:
‘Typeof’ is an operator which is used to return a string description of the type of a variable.
45. Which keywords are used to handle exceptions?
document.write(“Welcome”) is used to print the text – Welcome in the screen.
47. What is the use of blur function?
Blur function is used to remove the focus from the specified object.
48. What is variable typing?
Variable typing is used to assign a number to a variable and then assign string to the same variable. Example is as follows:
The ‘Navigator.appversion’ is used to find the name of the operating system in the client machine.
There are three types of errors:
- Load time errors: Errors which come up when loading a web page like improper syntax errors are known as Load time errors and it generates the errors dynamically.
- Run time errors: Errors that come due to misuse of the command inside the HTML language.
- Logical Errors: These are the errors that occur due to the bad logic performed on a function which is having different operation.
The push method is used to add or append one or more elements to the end of an Array. Using this method, we can append multiple elements by passing multiple arguments
Unshift method is like push method which works at the beginning of the array. This method is used to prepend one or more elements to the beginning of the array.
54. How are object properties assigned?
Properties are assigned to objects in the following way –
Strict mode can be enabled by adding the string literal “use strict” above the file. This can be illustrated by the given example:
The status can be acquired as follows –
If the CheckBox will be checked, this alert will return TRUE.
57. How can the OS of the client machine be detected?
The navigator.appVersion string can be used to detect the operating system on the client machine.
58. Explain window.onload and onDocumentReady?
The onload function is not run until all the information on the page is loaded. This leads to a substantial delay before any code is executed.
onDocumentReady loads the code just after the DOM is loaded. This allows early manipulation of the code.
Closure is a locally declared variable related to a function which stays in memory when the function has returned.
A value can be appended to an array in the given manner –
arr[arr.length] = value;
61. Explain the for-in loop?
The for-in loop is used to loop through the properties of an object.
The syntax for the for-in loop is –
A function that is declared without any named identifier is known as an anonymous function. In general, an anonymous function is inaccessible after its declaration.
Anonymous function declaration –
The function .call() and .apply() are very similar in their usage except a little difference. .call() is used when the number of the function’s arguments are known to the programmer, as they have to be mentioned as arguments in the call statement. On the other hand, .apply() is used when the number is not known. The function .apply() expects the argument to be an array.
The basic difference between .call() and .apply() is in the way arguments are passed to the function. Their usage can be illustrated by the given example.
*Operators are without the parenthesis.
This can be done by including the name of the required frame in the hyperlink using the ‘target’ attribute.
Break statement is used to come out of the current loop while the continue statement continues the current loop with a new recurrence.
69. Write the point of difference between web-garden and a web-farm?
Both web-garden and web-farm are web hosting systems. The only difference is that web-garden is a setup that includes many processors in a single server while web-farm is a larger setup that uses more than one server.
70. 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”
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.
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.
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.
Nested functions: The functions, which are defined inside other functions, are called Nested functions. They are called ‘everytime’ the main function is invoked.
- 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.
Screen objects are used to read the information from the client’s screen. The properties of screen objects are –
- AvailHeight: 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
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 –
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.
The unescape() function is very important as it decodes the coded string.
It works in the following way. For example:
80. 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.
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.
82. What does the following statement declares?
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.
Add “<!–” without the quotes in the code just after the <script> tag.
Add “//–>” without the quotes in the code just before the <script> tag.
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