typeof 0              // number
typeof true           // boolean
typeof 'Hello'        // string
typeof Math           // object
typeof null           // object  !!
typeof Symbol('Hi')   // symbol (New ES6)

var name = 'Joey';
if (name) {
  console.log(name + " doesn't share food!")  // Joey doesn’t share food!
}

Boolean(null)         // false
Boolean('hello')      // true 
Boolean('0')          // true 
Boolean(' ')          // true 
Boolean([])           // true 
Boolean(function(){}) // true

1 + "2" = "12"
"" + 1 + 0 = "10"
"" - 1 + 0 = -1
"-9\n" + 5 = "-9\n5"
"-9\n" - 5 = -14
"2" * "3" = 6
4 + 5 + "px" = "9px"
"$" + 4 + 5 = "$45"
"4" - 2 = 2
"4px" - 2 = NaN
null + 1 = 1

2 == '2'            // True
2 === '2'           // False
undefined == null   // True
undefined === null  // False

let a = '0';
console.log(Boolean(a)); // True
let b = false;
console.log(Boolean(b)); // False
```	

你認為下面的相等判斷會輸出什麼值呢?
```js
console.log(a == b);

'0' == false   (1)
'0' == 0       (2)
 0  == 0       (3)

false == ""  // true
false == []  // true
false == {}  // false
"" == 0      // true
"" == []     // true
"" == {}     // false
0 == []      // true
0 == {}      // false
0 == null    // false