> For the complete documentation index, see [llms.txt](https://ricardomol.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ricardomol.gitbook.io/notes/frontend/untitled/assorted.md).

# Assorted

## `typeof bar === "object"` to determine if `bar` is an object

`typeof bar === "object"` is a reliable way of checking if `bar` is an object

But:**`null` is also considered an object!**

Therefore:

```javascript
var bar = null;
console.log(typeof bar === "object");  // logs true!
```

Solution: **also check if `bar` is `null`**:

```javascript
console.log((bar !== null) && (typeof bar === "object")); 
// logs false
```

There are two other things worth noting:

First, the **above solution will return `false` if `bar` is a function**. In most cases, this is the desired behavior, but in situations where you want to also return `true` for functions, you could amend the above solution to be:

```
console.log((bar !== null) && ((typeof bar === "object") || (typeof bar === "function")));
```

Second, the **above solution will return `true` if `bar` is an array** (e.g., if `var bar = [];`). In most cases, this is the desired behavior, since arrays are indeed objects, but in situations where you want to also `false` for arrays, you could amend the above solution to be:

```
console.log((bar !== null) && (typeof bar === "object") && (toString.call(bar) !== "[object Array]"));
```

However, there’s one other alternative that returns `false` for nulls, arrays, and functions, but `true` for objects:

```
console.log((bar !== null) && (bar.constructor === Object));
```

Or, if you’re using jQuery:

```
console.log((bar !== null) && (typeof bar === "object") && (! $.isArray(bar)));
```

**ES6** makes the array case quite simple, including its own null check with **Array.isArray()**:

```javascript
console.log(Array.isArray(bar));
```

## NaN

### Definition

Represents a value that is not a number.

Results from an operation that could not be performed.

### Gotchas

1. Although `NaN` means “not a number”, **its type is, believe it or not, `Number`**:

```javascript
console.log(typeof NaN === "number");  // logs "true"
```

2\. `NaN` **compared to anything – even itself! – is false**:

```javascript
console.log(NaN === NaN);  // logs "false"
```

### Testing whether a number is equal to NaN

**built-in function `isNaN()`**[ (imperfect solution](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN#Confusing_special-case_behavior))

`value !== value` only true if the value is NaN

**More reliable solution: ES6**  [**`Number.isNaN()`**](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN) function