# APIs with Express (axios)

### Objectives

* Describe the purpose of using an API on the backend.
* Create an application that uses an API and the `axios` module.

In order to get around issues such as [CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS) and API access control, we can communicate with other servers through our server. In this case, our server acts as both a client and a server. We'll be doing some requests using the `axios` Node module.

To use the module, install it using npm.

```bash
npm i axios
```

Here's an example from NPM's homepage for the `axios` module. Let's take a look at it.

```javascript
const axios = require('axios');

// Make a request for a user with a given ID
axios.get('/user?ID=12345')
  .then(function (response) {
    // handle success
    console.log(response);
  })
  .catch(function (error) {
    // handle error
    console.log(error);
  })
  .finally(function () {
    // always executed
  });
```

Identify what's necessary for making a server-side request.

* axios module import
* axios.get function
  * URL
  * any other data or headers that need to be passed (optional)
  * `then` promise (the code that runs once the request finishes)
    * handle a success
    * catch any raised exceptions or errors (optional)
    * run something at the end regardless (optional)

### Incorporating `axios` into Express

In order to incorporate the `axios` module into Express, we can set up a basic Express application and place the request code inside a route.

This can be done by creating a new directory, running `npm init`, then installing the correct dependencies (refer back to the notes if you forgot). Here's an example app.

#### Example

**server.js**

```javascript
const express = require('express');
const axios = require('axios');
const app = express();

app.get('/', function(req, res) {
  axios.get('http://www.google.com')
    .then(function (response) {
      // handle success
      console.log(response);
    })
});

app.listen(3000);
```

Note that this app sends out the HTML for <http://www.google.com>, minus the images due to the images having links **relative** to <http://localhost:3000>

Let's use a more useful source of data that we can parse, like OMDB (Open Movie Database)

### Fetching JSON data

Let's modify the example above to make a request to OMDB's API. [OMDB Link](http://www.omdbapi.com/)

**We'll be using this endpoint:** <http://www.omdbapi.com/?s=star+wars&apikey=yourkey123>

#### Modified Example

**server.js**

```javascript
const express = require('express');
const axios = require('axios');
const app = express();

app.get('/', function(req, res) {
  var qs = {
    params: {
      s: 'star wars',
      apikey: 'YOUR-KEY-HERE'
    }
  };

  axios.get('http://www.omdbapi.com', qs)
    .then(function (response) {
      // handle success
      console.log(response.data);
    })
});

app.listen(3000);
```

**API Keys**

Notice that OMDB API has a key requirement for their API. That's okay, it just means we'll need to register for a key real quick before running the example. Don't worry - it's free and only takes a few minutes. Lots of APIs will require keys, so let's get into the habit!

> Protip: Never share your API keys! These should go in `.env` files and never, ever be pushed up to Github or anywhere else online. The `.env` file can be added to your `.gitignore` file to make git ignore it!

**Things to Note**

* In order to pass a query string to OMDB, we can create an object with key-value pairs.
  * This object **MUST** contain a key named "params" that is an object containing the key-value pairs you want to send in the query string.
* After getting the response back, we need to look inside `response.data` to see what was actually returned from the api. That's where axios puts the data. The `response` object you get back from axios is actually a wrapper that contains the api data among other things.
* It's very important to call `res.send` in the correct place (the axios 'then' promise)
  * Try putting `res.send` outside of the 'then'. You'll get an error!

## Additional Topics

* [API Information](https://romebell.gitbook.io/sei-802/resources/apis)
* [Using APIs with Client/Secret Keys (Foreman)](https://romebell.gitbook.io/sei-802/deployment-and-config/deploy-rails/foreman)


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