Javascripts variables are dynamically typed. While == operator converts each to a string representation before comparision, === compares without converting. For example,

1 == '1'; // true
1 === '1'; // false

1 == [1]; // true
1 === [1]; // false

Primitive Data Types

• undefined
• null
• boolean
• number: includes Infinity and NaN
• string
• symbol
• object: includes arrays

Truthy and Falsy

• The following values are always falsy:
  • false
  • 0
  • ’’ or “”
  • null
  • undefined
  • NaN
• Everything else is truthy.

Loose Equality Comparisons With ==

• false, 0, ‘’, and “” are all equivalent.
• null and undefined are equivalent.
• NaN is not equivalent to anything, even itself.
• Infinity and {} is not equivalent to anything excep itself.
• [] is equivalent to false, 0 and ‘’.

Strict Equality Comparisons With ===

Except NaN is not quivalent to ifseft, anything equivalent to itself but not others.

Quiz 1

What is the result of executing this code?

var a = 0 || [] || 1;
var b = NaN == NaN;
console.log(a, b);

Quiz 2

Suppose that I want to call foo() when x and y are identical. The following code is correct?

if (x === y) {
  foo();
}

If not, please fix it!