61⟩ Which symbol is used for comments in Javascript?
// for Single line comments and
/* Multi
Line
Comment
*/
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208 Expert JavaScript Developer Questions And Answers
62⟩ What is a prompt box in JavaScript?
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.
63⟩ Which company developed JavaScript?
Netscape is the software company who developed JavaScript.
64⟩ 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
65⟩ 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.
66⟩ 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]"));
Or, if you're using jQuery:
console.log((bar !== null) && (typeof bar === "object") && (! $.isArray(bar)));
67⟩ Define event bubbling in JavaScript?
JavaScript allows DOM elements to be nested inside each other. In such a case, if the handler of the child is clicked, the handler of parent will also work as if it were clicked too.
68⟩ How can a value be appended to an array?
A value can be appended to an array in the given manner -
arr[arr.length] = value;
69⟩ Which keyword is used to print the text in the screen?
document.write("Welcome") is used to print the text - Welcome in the screen.
70⟩ Mention what is the disadvantage of using innerHTML in JavaScript?
If you use innerHTML in JavaScript the disadvantage is
► 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
71⟩ What is the use of Void(0)?
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.
72⟩ How can you convert the string of any base to integer in JavaScript?
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 -
parseInt ("4F", 16);
73⟩ 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.
74⟩ 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.
75⟩ Does JavaScript support automatic type conversion?
Yes JavaScript does support automatic type conversion, it is the common way of type conversion used by JavaScript developers
76⟩ What are JavaScript types?
Following are the JavaScript types:
Number
String
Boolean
Function
Object
Null
Undefined
77⟩ How are object properties assigned?
Properties are assigned to objects in the following way -
obj["class"] = 12;
or
obj.class = 12;
78⟩ How generic objects can be created?
Generic objects can be created as:
var I = new object();
79⟩ How to find operating system in the client machine using JavaScript?
The 'Navigator.appversion' is used to find the name of the operating system in the client machine.
80⟩ What is the data type of variables in JavaScript?
All variables in the JavaScript are object data types.
