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Solutions: Object Oriented JavaScript: Chapter 2: Primitives

JavaScript experts can skip this.  
While reading the book, Object Oriented JavaScript by Stoyan Stefanov, I thought it would be a good idea to just solve the exercises presented in the book and store the solutions away. Takes me back to my school days when I was serious about learning stuff :) This will be a multi-part blog, with each blog entry solving exercises presented in one chapter of the book. The entire set of solutions will be eventually made available in my JavaScript site. So here goes ...
Chapter 2: Primitive Data Types, Arrays, Loops and Conditions

1. What is the result of executing each of these lines in the console? Why?
>> var a; typeof a;
undefined  // a has not been defined with any value

>> var s = '1s'; s++;
NaN  // converting 1s to a number is ambiguous with addition

>> !!"false"
true  // "false" is a valid string

>> !!undefined
false  //undefined is a falsy

>> typeof -Infinity
"number"  //this is th…