Java Script Interview Question and Answer

41. How to print a web page using javascript?
JavaScript helps you to implement this functionality using print function of window object. The JavaScript print function window.print() will print the current web page when executed.

42. 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.

43. 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.

44. What are the various functional components in JavaScript?
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.

45. How can we detect OS of the client machine using JavaScript?
The navigator.appVersion string can be used to detect the operating system on the client machine.

46. What is the significance, and what are the benefits, of including ‘use strict’ at the beginning of a JavaScript source file?
The short and most important answer here is that use strict is a way to voluntarily enforce stricter parsing and error handling on your JavaScript code at runtime. Code errors that would otherwise have been ignored or would have failed silently will now generate errors or throw exceptions. In general, it is a good practice.
Some of the key benefits of strict mode include:
Makes debugging easier. Code errors that would otherwise have been ignored or would have failed silently will now generate errors or throw exceptions, alerting you sooner to problems in your code and directing you more quickly to their source.
Prevents accidental globals. Without strict mode, assigning a value to an undeclared variable automatically creates a global variable with that name. This is one of the most common errors in JavaScript. In strict mode, attempting to do so throws an error.
Eliminates this coercion. Without strict mode, a reference to a this value of null or undefined is automatically coerced to the global. This can cause many headfakes and pull-out-your-hair kind of bugs. In strict mode, referencing a a this value of null or undefined throws an error.

47. Is it possible to break JavaScript Code into several lines?
Breaking within a string statement can be done by the use of a backslash, ‘\’, at the end of the first line

48. Explain the working of timers in JavaScript? Also elucidate the drawbacks of using the timer, if any?
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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