Java Script Interview Question and Answer

33. What is an undefined value in JavaScript?
Undefined value means the
Variable used in the code doesn’t exist
Variable is not assigned to any value
Property doesn’t exist

34. What is the use of type of operator?
‘Typeof’ is an operator which is used to return a string description of the type of a variable.

35. What is unshift method in JavaScript?
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.

36. Describe the properties of an anonymous function in JavaScript?
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.

37. What is the role of break and continue statements?
Break statement is used to come out of the current loop while the continue statement continues the current loop with a new recurrence.

38. 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.

39. 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.

40. What is Date object in JavaScript?
The Date object is a datatype built into the JavaScript language. Date objects are created with the new Date( ).
Once a Date object is created, a number of methods allow you to operate on it. Most methods simply allow you to get and set the year, month, day, hour, minute, second, and millisecond fields of the object, using either local time or UTC (universal, or GMT) time.

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