Ggtcf

Learning ExpressJS here.
I have a get route that expects query params i.e.

app.get('/api', (req, res) => 
 res.send( name: req.query.name, age: req.query.age, club: req.query.club )
)

On postman the following http://localhost:5000/api?name=Messi&age=31&club=Barcelona

returns 200 with the res.body as:

 "name": "Messi",
 "age": "31",
 "club": "Barcelona"

Question

How could I write a custom validation where:

• If the requested query param doesn't exist: status 400


• If any of the params are missing i.e (name, age, club) return a response saying that whichever missing param (name, age, and/or age) is required

You can build an easy validation middleware.

function validateQuery(fields) 

 return (req, res, next) => 

 for(const field of fields) 
 if(!req.query[field]) // Field isn't present, end request
 return res
 .status(400)
 .send(`$field is missing`);
 
 

 next(); // All fields are present, proceed

 ;



app.get('/api', validateQuery(['name', 'age', 'club']), (req, res) => 
 // If it reaches here, you can be sure that all the fields are not empty.
 res.send( name: req.query.name, age: req.query.age, club: req.query.club )
)

You can also use a third party module for validating requests.

• Express Validator


• 
  Express Superstruct (I'm the author)

You need to check value of every params value

If(typeof req.query.name == 'undefined' )
 res.status(400).send('name is missing') 

Check for every value

The above answers are correct, but as someone who has worked with scalable and maintenable APIs, I'd recommend standardizing the validation process of you API using JSON Schemas to define the expected input, and AJV to validate these schemas.

Example usage:

const Ajv = require('ajv');
const express = require('express');

const app = express();

app.get('/api', (req, res) => 

 // define precisely the expected shape of the request
 const schema = 
 type: 'object',
 properties: 
 name: type: 'string' ,
 age: type: 'string' ,
 club: type: 'string' 
 ,
 required: ['name', 'age', 'club']
 

 // validate the request
 const ajv = new Ajv();
 const valid = ajv.validate(schema, req.query);
 if(!valid) res.status(400).send(ajv.errors);

 // request is valid. Do whatever
 res.send(req.query);

)

app.listen(8080, () => console.log('Server listening on port 8080'));

Response to /api:

[
 
 "keyword": "required",
 "dataPath": "",
 "schemaPath": "#/required",
 "params": 
 "missingProperty": "name"
 ,
 "message": "should have required property 'name'"
 
]

Response to /api?name=messi&age=10&club=barcelona:

 "name": "messi",
 "age": "10",
 "club": "barcelona"

Yes it takes a little bit more code, but trust me, it's the way to go if you want to prepare your app for complex and scalable API validation.