JavaScript Interview Questions and Answers | JavaScript Interview Sample Questions

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. What are JavaScript types? – Number, String, Boolean, Function, Object, Null, Undefined.
3. 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);
4. What does isNaN function do? – Return true if the argument is not a number.
5. What is negative infinity? – It’s a number in JavaScript, derived by dividing negative number by zero.
6. What boolean operators does JavaScript support? – &&, || and !
7. What does “1″+2+4 evaluate to? – Since 1 is a string, everything is a string, so the result is 124.
8. 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.
9. What looping structures are there in JavaScript? – for, while, do-while loops, but no foreach.
10. How do you create a new object in JavaScript? – var obj = new Object(); or var obj = {};
11. How do you assign object properties? – obj["age"] = 17 or obj.age = 17.
12. What’s a way to append a value to an array? – arr[arr.length] = value;
13. What is this keyword? – It refers to the current object.

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