eolas/Programming_Languages/NodeJS/REST_APIs/2_POST.md

---
tags:
  - Programming_Languages
  - backend
  - node-js
  - express
  - REST
  - apis
---

# Creating a REST API with Node and Express: POST requests

To demonstrate the handling of POST requests, we will create a handler that add a new element to the array of courses.

```js
app.post('/api/courses', (req, res) => {
	const course = {
		id: courses.length + 1,
		name: req.body.name
	}
	courses.push(course);
	res.send(course)

})
```

Here we use the body that is sent from the client and isolate the field `name`. This presupposes that the client is sending us data with the following shape as the body:

```json
{
	"name": "Biology and Life Sciences"
}	
```

To execute the PUT request from the frontend:

```js
const addCourse = async (newCourse) => {
  try {
    const resp = await axios.post("http://localhost:3000/api/courses", {
      name: newCourse,
    });
    console.log(resp.data);
  } catch (err) {
    console.error(err);
  }
};
addCourse("Biology and Life Sciences");
```

Which returns: 

```js
{ id: 4, name: 'Biology and Life Sciences' }
```

The `id` is added by the server, not the client. Having created the new value we add it to our `courses` array. (In reality we would be creating a new entry in a database.) Then we follow the convention of returning the new value back to the client. 

## Validation

We should accept alterations to the database that are not first validated. We can use the [Joi validator](/Programming_Languages/NodeJS/REST_APIs/Validation.md) to vet the request:

```js
function validateCourse(course) {
  const schema = Joi.object({
    name: Joi.string().min(3).required(),
  });

  const { error } = schema.validate(course);
  return error;
}
```
We can then add the validation as part of our general error handling:

```js
app.post('/api/courses', (req, res) => {
	const course = {
		id: courses.length + 1,
		name: req.body.name
	}
  const { error } = schema.validate(req.body);
  if (error) return error.details.map((joiErr) => res.status(400).send(joiErr.message));
  
  courses.push(course);
  res.send(course)
})
```