Xcidic Coding Guidelines > JavaScript Style Guide > ES5 > Types

Types

Primitives: When you access a primitive type you work directly on its value.
- string
- number
- boolean
- null
- undefined
```
var foo = 1;
var bar = foo;

bar = 9;

console.log(foo, bar); // => 1, 9
```
Complex: When you access a complex type you work on a reference to its value.
- object
- array
- function
```
var foo = [1, 2];
var bar = foo;

bar[0] = 9;

console.log(foo[0], bar[0]); // => 9, 9
```