Mindtree JavaScript Most Frequently Asked Latest Interview Questions Answers
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.
Explain how can you submit a form using JavaScript?
To submit a form using JavaScript use document.form[0].submit();
document.form[0].submit();
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
How can the style/class of an element be changed?
It can be done in the following way:
document.getElementById(“myText”).style.fontSize = “20?;
or
document.getElementById(“myText”).className = “anyclass”;
Explain how to read and write a file using JavaScript?
There are two ways to read and write a file using JavaScript
Using JavaScript extensions
Using a web page and Active X objects
What are all the looping structures in JavaScript?
Following are looping structures in Javascript:
For
While
do-while loops
What is called Variable typing in Javascript?
Variable typing is used to assign a number to a variable and the same variable can be assigned to a string.
Example
i = 10;
i = "string";
This is called variable typing.
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);
Explain the difference between “==” and “===”?
“==” 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.
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.
Explain how to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion string (property) should be used.
What do mean by NULL in Javascript?
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.
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.
What will be the output of the following code:
for (var i = 0; i < 5; i++) {
setTimeout(function() { console.log(i); }, i * 1000 );
}
Explain your answer. How could the use of closures help here?
The code sample shown will not display the values 0, 1, 2, 3, and 4 as might be expected; rather, it will display 5, 5, 5, 5, and 5.
The reason for this is that each function executed within the loop will be executed after the entire loop has completed and all will therefore reference the last value stored in i, which was 5.
Closures can be used to prevent this problem by creating a unique scope for each iteration, storing each unique value of the variable within its scope, as follows:
for (var i = 0; i < 5; i++) {
(function(x) {
setTimeout(function() { console.log(x); }, x * 1000 );
})(i);
}
This will produce the presumably desired result of logging 0, 1, 2, 3, and 4 to the console.
In an ES2015 context, you can simply use let instead of var in the original code:
for (let i = 0; i < 5; i++) {
setTimeout(function() { console.log(i); }, i * 1000 );
What would the following lines of code output to the console?
console.log("0 || 1 = "+(0 || 1));
console.log("1 || 2 = "+(1 || 2));
console.log("0 && 1 = "+(0 && 1));
console.log("1 && 2 = "+(1 && 2));
Explain your answer.
The code will output the following four lines:
0 || 1 = 1
1 || 2 = 1
0 && 1 = 0
1 && 2 = 2
In JavaScript, both || and && are logical operators that return the first fully-determined “logical value” when evaluated from left to right.
The or (||) operator. In an expression of the form X||Y, X is first evaluated and interpreted as a boolean value. If this boolean value is true, then true (1) is returned and Y is not evaluated, since the “or” condition has already been satisfied. If this boolean value is “false”, though, we still don’t know if X||Y is true or false until we evaluate Y, and interpret it as a boolean value as well.
Accordingly, 0 || 1 evaluates to true (1), as does 1 || 2.
The and (&&) operator. In an expression of the form X&&Y, X is first evaluated and interpreted as a boolean value. If this boolean value is false, then false (0) is returned and Y is not evaluated, since the “and” condition has already failed. If this boolean value is “true”, though, we still don’t know if X&&Y is true or false until we evaluate Y, and interpret it as a boolean value as well.
However, the interesting thing with the && operator is that when an expression is evaluated as “true”, then the expression itself is returned. This is fine, since it counts as “true” in logical expressions, but also can be used to return that value when you care to do so. This explains why, somewhat surprisingly, 1 && 2 returns 2 (whereas you might it expect it to return true or 1).
What will be the output when the following code is executed? Explain.
console.log(false == '0')
console.log(false === '0')
The code will output:
true
false
In JavaScript, there are two sets of equality operators. The triple-equal operator === behaves like any traditional equality operator would: evaluates to true if the two expressions on either of its sides have the same type and the same value. The double-equal operator, however, tries to coerce the values before comparing them. It is therefore generally good practice to use the === rather than ==. The same holds true for !== vs !=.
What is the output out of the following code? Explain your answer.
var a={},
b={key:'b'},
c={key:'c'};
a[b]=123;
a[c]=456;
console.log(a[b]);
The output of this code will be 456 (not 123).
The reason for this is as follows: When setting an object property, JavaScript will implicitly stringify the parameter value. In this case, since b and c are both objects, they will both be converted to "[object Object]". As a result, a[b] anda[c] are both equivalent to a["[object Object]"] and can be used interchangeably. Therefore, setting or referencing a[c] is precisely the same as setting or referencing a[b].
What is the name of object used for AJAX request?
XmlHttpRequest object is used for Ajax requests.
What is prerequisite for Update Panel in Ajax?
Script Manager is pre-requisite to use Update Panel controls.
How many update panel can be used per page?
There are no restrictions on the number of update panels per page.
How can you find out that an AJAX request has been completed?
ReadyState property is used to check whether AJAX request has been completed. If the property is equal to four, then the request has been completed and data is available.
Is javascript knowledge is required to do Ajax?
Yes, if you plan to develop new AJAX functionality for your web application.
What are all the browsers support AJAX?
Following browsers support AJAX:
Internet Explorer 5.0 and above
Opera 7.6 and above
Netscape 7.1 and above
Safari 1.2 and above.
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.
Explain how can you submit a form using JavaScript?
To submit a form using JavaScript use document.form[0].submit();
document.form[0].submit();
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
How can the style/class of an element be changed?
It can be done in the following way:
document.getElementById(“myText”).style.fontSize = “20?;
or
document.getElementById(“myText”).className = “anyclass”;
 |
| Mindtree JavaScript Most Frequently Asked Latest Interview Questions Answers |
Explain how to read and write a file using JavaScript?
There are two ways to read and write a file using JavaScript
Using JavaScript extensions
Using a web page and Active X objects
What are all the looping structures in JavaScript?
Following are looping structures in Javascript:
For
While
do-while loops
What is called Variable typing in Javascript?
Variable typing is used to assign a number to a variable and the same variable can be assigned to a string.
Example
i = 10;
i = "string";
This is called variable typing.
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);
Explain the difference between “==” and “===”?
“==” 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.
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.
Explain how to detect the operating system on the client machine?
In order to detect the operating system on the client machine, the navigator.appVersion string (property) should be used.
What do mean by NULL in Javascript?
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.
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.
What will be the output of the following code:
for (var i = 0; i < 5; i++) {
setTimeout(function() { console.log(i); }, i * 1000 );
}
Explain your answer. How could the use of closures help here?
The code sample shown will not display the values 0, 1, 2, 3, and 4 as might be expected; rather, it will display 5, 5, 5, 5, and 5.
The reason for this is that each function executed within the loop will be executed after the entire loop has completed and all will therefore reference the last value stored in i, which was 5.
Closures can be used to prevent this problem by creating a unique scope for each iteration, storing each unique value of the variable within its scope, as follows:
for (var i = 0; i < 5; i++) {
(function(x) {
setTimeout(function() { console.log(x); }, x * 1000 );
})(i);
}
This will produce the presumably desired result of logging 0, 1, 2, 3, and 4 to the console.
In an ES2015 context, you can simply use let instead of var in the original code:
for (let i = 0; i < 5; i++) {
setTimeout(function() { console.log(i); }, i * 1000 );
What would the following lines of code output to the console?
console.log("0 || 1 = "+(0 || 1));
console.log("1 || 2 = "+(1 || 2));
console.log("0 && 1 = "+(0 && 1));
console.log("1 && 2 = "+(1 && 2));
Explain your answer.
The code will output the following four lines:
0 || 1 = 1
1 || 2 = 1
0 && 1 = 0
1 && 2 = 2
In JavaScript, both || and && are logical operators that return the first fully-determined “logical value” when evaluated from left to right.
The or (||) operator. In an expression of the form X||Y, X is first evaluated and interpreted as a boolean value. If this boolean value is true, then true (1) is returned and Y is not evaluated, since the “or” condition has already been satisfied. If this boolean value is “false”, though, we still don’t know if X||Y is true or false until we evaluate Y, and interpret it as a boolean value as well.
Accordingly, 0 || 1 evaluates to true (1), as does 1 || 2.
The and (&&) operator. In an expression of the form X&&Y, X is first evaluated and interpreted as a boolean value. If this boolean value is false, then false (0) is returned and Y is not evaluated, since the “and” condition has already failed. If this boolean value is “true”, though, we still don’t know if X&&Y is true or false until we evaluate Y, and interpret it as a boolean value as well.
However, the interesting thing with the && operator is that when an expression is evaluated as “true”, then the expression itself is returned. This is fine, since it counts as “true” in logical expressions, but also can be used to return that value when you care to do so. This explains why, somewhat surprisingly, 1 && 2 returns 2 (whereas you might it expect it to return true or 1).
What will be the output when the following code is executed? Explain.
console.log(false == '0')
console.log(false === '0')
The code will output:
true
false
In JavaScript, there are two sets of equality operators. The triple-equal operator === behaves like any traditional equality operator would: evaluates to true if the two expressions on either of its sides have the same type and the same value. The double-equal operator, however, tries to coerce the values before comparing them. It is therefore generally good practice to use the === rather than ==. The same holds true for !== vs !=.
What is the output out of the following code? Explain your answer.
var a={},
b={key:'b'},
c={key:'c'};
a[b]=123;
a[c]=456;
console.log(a[b]);
The output of this code will be 456 (not 123).
The reason for this is as follows: When setting an object property, JavaScript will implicitly stringify the parameter value. In this case, since b and c are both objects, they will both be converted to "[object Object]". As a result, a[b] anda[c] are both equivalent to a["[object Object]"] and can be used interchangeably. Therefore, setting or referencing a[c] is precisely the same as setting or referencing a[b].
What is the name of object used for AJAX request?
XmlHttpRequest object is used for Ajax requests.
What is prerequisite for Update Panel in Ajax?
Script Manager is pre-requisite to use Update Panel controls.
How many update panel can be used per page?
There are no restrictions on the number of update panels per page.
How can you find out that an AJAX request has been completed?
ReadyState property is used to check whether AJAX request has been completed. If the property is equal to four, then the request has been completed and data is available.
Is javascript knowledge is required to do Ajax?
Yes, if you plan to develop new AJAX functionality for your web application.
What are all the browsers support AJAX?
Following browsers support AJAX:
Internet Explorer 5.0 and above
Opera 7.6 and above
Netscape 7.1 and above
Safari 1.2 and above.
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