gistfile1.js

>>> 3+2
5

>>> typeof(3);
number

>>> typeof(3) === typeof(4.32);
true

>>> 5/0
Infinity

>>> 5/0;
Infinity

>>> 3/"bob"
NaN

>>> NaN === NaN;
false

>>> typeof(NaN);
number

>>> isNaN(NaN);
true

>>> x = 5
5

>>> var x = 5;
undefined

>>> isNaN(5);
false

>>> Math.pow(2,3);
8

>>> var first_name = "cindy";
undefined
>>> first_name
cindy
>>> typeof(first_name);
string

The var keyword assign the the value "cindy" to "first_name" and also assigns type as string.

>>> var hello;
undefined
>>> hello
undefined

>>> var y;
undefined
>>> y === "cool";
false
>>> y == "cool";
false

the value of y is equal to undefined which doesn't equal "cool".

>>> var first = "Bart";
undefined
>>> var last = "Simpson";
undefined
>>> first
Bart
>>> last
Simpson
>>> first + " " + last
Bart Simpson

Bart is a string and Simpson is a string. Both are operands concatenated by the operator +.

>>> "cool".length;
4

>>> "phat" === "phat";
true

>>> typeof("cats")
string

>>> 3 + "bob"
3bob

>>> String(3);
3

>>> 4.87 - .87
4

>>> x = 6 / "2"
3
>>> typeof(x);
number

javascript coerces "2" into a string to evaluate the expression. it wants to evaluate the expression!

under the hood JS is saying..

>>> Number("2");
2

>>> 3 * "bob"
NaN

>>> var x
undefined
>>> var y
undefined


>>> var hobby = "programming"
undefined
>>> hobby
programming

>>> var sport;
undefined

>>> sport === undefined;
true

>>> typeof("brogrammer");
string