Interview questions and answers : JavaScript

  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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