validationResult()

These methods are all available via require('express-validator').

validationResult(req)

• req: the express request object

Returns: a Result object

Extracts the validation errors from a request and makes them available in a Result object.

Each error returned by .array() and .mapped() methods has the following format by default:

{
  "msg": "The error message",
  "param": "param.name.with.index[0]",
  "value": "param value",
  // Location of the param that generated this error.
  // It's either body, query, params, cookies or headers.
  "location": "body",

  // nestedErrors only exist when using the oneOf function
  "nestedErrors": [{ ... }]
}

.withDefaults(options)

• options (optional): an object of options. Defaults to { formatter: error => error }

Returns: a new validationResult function, using the provided options

Creates a new validationResult()-like function with default options passed to the generated Result instance.

Below is an example which sets a default error formatter:

const { validationResult } = require('express-validator');

const myValidationResult = validationResult.withDefaults({
  formatter: error => {
    return {
      myLocation: error.location,
    };
  },
});

app.post('/create-user', yourValidationChains, (req, res) => {
  // errors will be like [{ myLocation: 'body' }, { myLocation: 'query' }], etc
  const errors = myValidationResult(req).array();
});

Result

An object that holds the current state of validation errors in a request and allows access to it in a variety of ways.

.isEmpty()

Returns: a boolean indicating whether this result object contains no errors at all.

app.post('/create-user', yourValidationChains, (req, res) => {
  const result = validationResult(req);
  const hasErrors = !result.isEmpty();
  // do something if hasErrors is true
});

.formatWith(formatter)

• formatter(error): the function to use to format when returning errors.
  The error argument is an object in the format of { location, msg, param, value, nestedErrors }, as described above.

Returns: a new Result instance

JavaScript

const { validationResult } = require('express-validator');
app.post('/create-user', yourValidationChains, (req, res, next) => {
  const errorFormatter = ({ location, msg, param, value, nestedErrors }) => {
    // Build your resulting errors however you want! String, object, whatever - it works!
    return `${location}[${param}]: ${msg}`;
  };
  const result = validationResult(req).formatWith(errorFormatter);
  if (!result.isEmpty()) {
    // Response will contain something like
    // { errors: [ "body[password]: must be at least 10 chars long" ] }
    return res.json({ errors: result.array() });
  }

  // Handle your request as if no errors happened
});

TypeScript

import { value validationResult, value ValidationError } from 'express-validator';
app.post('/create-user', yourValidationChains, (req, res, next) => {
  const errorFormatter = ({ location, msg, param, value, nestedErrors }: ValidationError) => {
    // Build your resulting errors however you want! String, object, whatever - it works!
    return `${location}[${param}]: ${msg}`;
  };
  const result = validationResult(req).formatWith(errorFormatter);
  if (!result.isEmpty()) {
    // Response will contain something like
    // { errors: [ "body[password]: must be at least 10 chars long" ] }
    return res.json({ errors: result.array() });
  }

  // Handle your request as if no errors happened
});

.array([options])

• options (optional): an object of options. Defaults to { onlyFirstError: false }

Returns: an array of validation errors.

Gets all validation errors contained in this result object.

If the option onlyFirstError is set to true, then only the first error for each field will be included.

.mapped()

Returns: an object where the keys are the field names, and the values are the validation errors

Gets the first validation error of each failed field in the form of an object.

.throw()

If this result object has errors, then this method will throw an exception decorated with the same validation result API.

try {
  validationResult(req).throw();
  // Oh look at ma' success! All validations passed!
} catch (err) {
  console.log(err.mapped()); // Oh noes!
}