JavaScript Interview Answers

1. What’s relationship between JavaScript and ECMAScript?

   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. How do you convert numbers between different bases in JavaScript?

   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);

3. What is negative infinity?

   It’s a number in JavaScript, derived by dividing negative number by zero.

4. What does "1"+2+4 evaluate to?

   Since 1 is a string, everything is a string, so the result is 124.

5. How about 2+5+"8"?

   Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it’s concatenation, so 78 is the result.

6. How do you create a new object in JavaScript?

   var obj = new Object(); or var obj = {};

7. What’s a way to append a value to an array?

   arr[arr.length] = value;

8. What are JavaScript types?

   Number, String, Boolean, Function, Object, Null, Undefined.

9. What does isNaN function do?

   Return true if the argument is not a number.

10. What boolean operators does JavaScript support?

    &&, || and !

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Answers sourced from www.techinterviews.com