---
layout: default
parent: Type helpers
grand_parent: Helpers

title: isNullOrEmpty
---

<script src="{{ site.baseurl }}{% link assets/dist/index.js %}"></script>

# Assert a lack of content

`isNullOrEmpty` works on objects that 'have items', so it can be used to check if
things like arrays or strings are empty, null or undefined.

It works on the following types:
 - string
 - array
 - [Enumerable](../../Enumerables/index.md)
 - anything that implements `{ length: number; }`
 - anything that implements `{ count: number; }`


Empty can be defined easily with examples.

> Note: Using TypeScript here for brevity.  

``` ts
 const empty: string = '';
 const empty: [] = [];
 const empty: IEnumerable<number> = Enumerable.empty();
```
<script>
    function executeExample(resultId, fn) {
        const el = document.getElementById(resultId);
        const value = fn();
        el.innerText += value+'\n';
    }
</script>


Here is an example using a string. When `greeting` has no value, we set a *default*
value of `'Hello'`.

<div class="code-example">
    <div>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-string-example-result', () => greet('world'))">Execute helloWorld</button>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-string-example-result', () => greet('Hi'))">Execute hiGreg</button>
        <p>
            <strong>Results</strong><br>
            <span id="isNullOrEmpty-string-example-result"></span>
        </p>
    </div>    
    <script>
        function greet(name, greeting) {
            if (utilities.isNullOrEmpty(greeting)) {
                greeting = 'Hello';
            }
            return `${greeting} ${name}.`;
        }
    </script>
</div>

```ts
function greet(name:string, greeting?:string) :string {
    if (!isNullOrEmpty(greeting)) {
        greeting = 'Hello';
    }
    return `${greeting} ${name}.`;
}
// "Hello world."
const helloWorld = greet('world');
// "Hi Greg."
const hiGreg = greet('Greg', 'Hi');
```

This example shows how you can use an array. When the datasource returns null or undefined, 
`getItems` will return an empty array. It does this so that the for-of does not need a null check.
Execution will pass through the for-of if the result is empty.

<div class="code-example">
    <div>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-array-example-result', () => getItems())">Get Items</button>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-array-example-result', () => clearItems())">Clear Items</button>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-array-example-result', () => createItems())">Create Items</button>
        <button type="button" class="btn" onclick="executeExample('isNullOrEmpty-array-example-result', () => removeItem())">Remove Items</button>
        <p>
            <strong>Results</strong><br>
            <span id="isNullOrEmpty-array-example-result"></span>
        </p>
    </div>    
    <script>
       let itemsisNullOrEmptyArrayExample = [1,2,3,4,5,6];       
       function getItems() {
            if (utilities.isNullOrEmpty(itemsisNullOrEmptyArrayExample)) {
                executeExample('isNullOrEmpty-array-example-result', ()=>"[LOG] `items` is null or empty. Returning empty array `[]`...");
                return itemsisNullOrEmptyArrayExample = [];
            }
            return itemsisNullOrEmptyArrayExample;
        }
        function createItems() {
            itemsisNullOrEmptyArrayExample.push(1,2,3,4,5,6);
            return itemsisNullOrEmptyArrayExample;
        }
        function clearItems() {
            return itemsisNullOrEmptyArrayExample = undefined;
        }
        function removeItem() {
            itemsisNullOrEmptyArrayExample.pop();
            return itemsisNullOrEmptyArrayExample;
        }
        execute('isNullOrEmpty-array-example-result', () => getItems());
    </script>
</div>

```ts
function getItems(name:string):[] {
    let items = dataSource.get(name);
    if (isNullOrEmpty(items)) {
        // return an empty arry regardless.
        // this method is always an Array.
        items = [];
    }
    // do other things
    return mapper.map(items);
}
// always has a value. It cannot be null.
const products = getItems('products');
// will not throw an exception for products being null
for (const product of products){
    ...
}
```