# Type-Checking Your Data

The Yahoo Global Object includes several useful type-checking methods in the `YAHOO.lang` object. Click the Check button in each row to evaluate the data.

Data | isObject | isArray | isFunction
--- | --- | --- | ---
`null``` |
`[] or new Array()` |
`{} or new Object()` |
`function Foo() {}` |
`new Foo()` |
`elem.getElementsByTagName('p')` |
`YAHOO.util.Dom. getElementsByClassName( 'foo','p',elem)` |