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# Boolean

Another important data type next to String and Number is Boolean. It has only two possible values:

`true`

and `false`

. You can calculate with Boolean values similar to numbers. JavaScript
has three Boolean operators: `&&`

(and), `||`

(or) and `!`

(not).
`&&`

links two Boolean values. If both values are `true`

, the result is `true`

.
In all other cases it is `false`

. With `||`

the result is `true`

,
if at least one of the two input values is `true`

. If both input values are `false`

,
the result is `false`

. `!`

is applied to a single Boolean value and inverts this value:
`!true`

is `false`

and `!false`

is `true`

.
```
var x1 = true && false;
var x2 = !x1;
var x3 = x1 || x2;
```

`x1`

is `false`

, `x2`

is `true`

and `x3`

is `true`

.## Exercise

Write a function

`nand`

that takes two Boolean values. If both values are `true`

,
the result should be `false`

. In the other cases the return should be `true`

.
The call `nand(true, true)`

should return `false`

. The calls `nand(true, false)`

,
`nand(false, true)`

and `nand(false, false)`

should return `true`

.
+ Hint

```
var nand = function(a, b) {
var and = a && b;
...
};
```

+ Solution

```
var nand = function(a, b) {
var and = a && b;
return !and;
};
```