JavaScript interview questions and answers – I

1. What’s relationship between JavaScript and ECMAScript?
Ans 1. ECMAScript is yet another name for JavaScript (other names include LiveScript). The current JavaScript that you see supported in browsers is ECMAScript revision 3.

2. What are JavaScript types?
Ans 2. Number, String, Boolean, Function, Object, Null, Undefined.

3. How do you convert numbers between different bases in JavaScript?
Ans 3. Use the parseInt() function, that takes a string as the first parameter, and the base as a second parameter. So to convert hexadecimal 3F to decimal, use parseInt (“3F”, 16);

4. What does isNaN function do?
Ans 4. Return true if the argument is not a number.

5. What is negative infinity?
Ans 5. It’s a number in JavaScript, derived by dividing negative number by zero.

6. What boolean operators does JavaScript support?
Ans 6. &&, || and !

7. What does “1”+2+4 evaluate to?
Ans 7. Since 1 is a string, everything is a string, so the result is 124.

8. How about 2+5+”8″?
Ans 8. Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it’s concatenation, so 78 is the result.

9. What looping structures are there in JavaScript?
Ans 9. for, while, do-while loops, but no foreach.

10. How do you create a new object in JavaScript?
Ans 10. var obj = new Object(); or var obj = {};

11. How do you assign object properties?
Ans 11. obj[“age”] = 17 or obj.age = 17.

12. What’s a way to append a value to an array?
Ans 13. arr[arr.length] = value;

13. What is this keyword?
Ans 13. It refers to the current object.

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