Validate input parameters in node.js requests

validate.js

var _ = require('underscore')
var util = require('util')

function validate(request) {
  var errors = []
  var values = {}

  var obj = {}

  function validator(param) {
    var vals = request[param]
    var self = {}

    self.string = function(field, required) {
      var value = vals[field]
      if ((_.isUndefined(value) && required) || !_.isString(value)) {
        errors.push({ field: field, message: util.format('`%s` is a required string field', field) })
      } else {
        values[field] = value
      }
      return obj
    }

    self.stringArray = function(field, required) {
      var value = vals[field]
      if ((_.isUndefined(value) && required) || !_.isArray(value)) {
        errors.push({ field: field, message: util.format('`%s` is a required array of strings', field) })
        return obj
      }
      if (!_.find(value, function(val) {
        if (!_.isString(val)) {
          errors.push({ field: field, message: util.format('`%s` must be an array of strings', field) })
          return true
        }
      })) {
        values[field] = value
      }
      return obj
    }

    self.number = function(field, required, min, max) {
      var value = vals[field]
      if (value != +value) {
        errors.push({ field: field, message: util.format('`%s` must be a number', field) })
        return obj
      }
      if (_.isUndefined(value) && required) {
        errors.push({ field: field, message: util.format('`%s` is a required number', field) })
        return obj
      }
      value = +value
      if (!_.isUndefined(min) && value < min) {
          errors.push({ field: field, message: util.format('`%s` must be higher than %d', field, min) })
      } else if (!_.isUndefined(max) && value > max) {
          errors.push({ field: field, message: util.format('`%s` must be lower than %d', field, max) })
      } else {
        values[field] = +value
      }
      return obj
    }

    self.integer = function(field, required, min, max) {
      var value = vals[field]
      if (value != Math.floor(+value)) {
        errors.push({ field: field, message: util.format('`%s` must be an integer', field) })
        return obj
      }
      if (_.isUndefined(value) && required) {
        errors.push({ field: field, message: util.format('`%s` is a required integer', field) })
        return obj
      }
      value = Math.floor(+value)
      if (!_.isUndefined(min) && value < min) {
          errors.push({ field: field, message: util.format('`%s` must be higher or equal than %d', field, min) })
      } else if (!_.isUndefined(max) && value > max) {
          errors.push({ field: field, message: util.format('`%s` must be lower or equal than %d', field, max) })
      } else {
        values[field] = +value
      }
      return obj
    }

    self.object = function(field, required) {
      var value = vals[field]
      if (!_.isObject(value)) {
        if (required) {
          errors.push({ field: field, message: util.format('`%s` is a required string field', field) })
          return obj
        }
      } else {
        values[field] = value
      }
      return obj
    }

    return self
  }

  ;['body', 'query', 'params'].forEach(function(key) {
    obj[key] = validator(key)
  })
  obj.end = function(callback) {
    callback(errors.length > 0 ? _.groupBy(errors, function(err) {
      var field = err.field
      delete err.field
      return field
    }) : null, values)
  }

  return obj
}


// example
validate(req)
  .body.string('some-string-param', true)
  .body.stringArray('some-array-param', true)
  .body.number('a-number-param', true)
  .body.integer('an-integer-param', true, 0, 100)
  .end(function(errors, values) {
    // errors: validation errors if any
    // values: object with accepted values
    console.log('errors', errors, values)
  })