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JavaScript Interview Questions and Answers

Ques 26. Explain String functions in Javascript.

Ans. a class defines a new type (formally, Abstract Data Type)
encapsulates data (properties) and operations on that data (methods)

a String encapsulates a sequence of characters, enclosed in quotes

properties include
length : stores the number of characters in the string

methods include
charAt(index) : returns the character stored at the given index
(as in C++/Java, indices start at 0)
substring(start, end) : returns the part of the string between the start
(inclusive) and end (exclusive) indices
toUpperCase() : returns copy of string with letters uppercase
toLowerCase() : returns copy of string with letters lowercase

to create a string, assign using new or just make a direct assignment (new is implicit)

word = new String(\"foo\"); word = \"foo\";

properties/methods are called exactly as in C++/Java

word.length word.charAt(0)

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Ques 27. Tell us about local variables.
Ans. If needed, you can declare local variables within a function.

local variable is visible only within the function body after it’s declared.

Commonly used to store results of an intermediate calculation.

function findMaxValue(num1, num2,num3) {
var tempMax; //local var

if (num1 >= num2) {
tempMax = num1;

else {
tempMax = num2;

if(num3 >= tempMax) {
tempMax = num3;

return tempMax;

} //end function
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Ques 28. Explain Global Variables in Javascript.
Ans. Global variables are those declared outside of functions
Global variables are ‘visible’ from anywhere in the program, including inside functions

var globalHello = “Hello!”;

function writeHello() {
// outputs “Hello!”
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Ques 29. What are primitives in Javascript?
Ans. Boolean, string and number.
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Ques 30. How do you submit a form using Javascript?
Ans. Use document.forms[0].submit();
(0 refers to the index of the form – if you have more than one form in a page, then the first one has the index 0, second has index 1 and so on).
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