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A lightweight, chaining validation library.

  • Zero dependencies. Can be used in browsers, Node, and Mongo/Couch Map/Reduce functions.
  • Recursively test JSON data structures.
  • Easy to extend with your own validations.
  • Excellent test coverage (run npm test).
    var Valid = require('valid');
    var inRange = Valid.number().min(4).max(9)
    inRange.check(7)            // returns nothing -- no errors
    inRange.check('7')          // returns "must be a number"
    inRange.check(12)           // returns "must be less than or equal to 9"

    Valid.optional().string().check(null);       // can be null, undefined, or a string
    Valid.array(Valid.integer()).check([1,2,3]);   // checks each item in the array

    // test JSON structures:
    var Schema = {
        Name:     Valid.notBlank(),
        Address: {
            State:    /^[A-Z][A-Z]$/,  // shortcut for Valid.match(/^[A-Z][A-Z]$/)
            Country:  "US"

    var data = {
        Name:     "Jed",
        Numbers:  [1, 9, 25],
        Address: {
            State:    "CA",
            Country:  "US"


    // Easily define your own validations:
    Valid.isPowerOfTen = Valid.mod(10).message("should be a power of ten).define();


This library is scary new.

  • terminology: exists/notExists, and oneOf/notOneOf vs. in/notIn
  • pass a json schema to array()? factor into RunSubtest & have everything call this.
  • npm publish
  • Pass error message to Valid constructor? make errorMessage a synonym for message?
  • test coverage?
  • write an assertion function? Valid.assert(12).integer().min(5);
  • convert to using nested functions instead of the __queue array?
  • 'not' should try to modify the error message on the way through
  • do a doctest somehow


Valid allows you to declare a validation and run it against any number of values:

    var validation = Valid.integer().even().min(6);
    validation.check(9);      // returns "9 is not even"
    validation.isValid(10);   // returns true.

check() returns undefined if the validation succeeds, a string like "should not be null" if it fails, or an error object for JSON validations (see Errors below). isValid() just returns true or false.

Built-In Validations

This list is probably incomplete but the code at the bottom of valid.js should be reasonably readable.

  • Presence: defined(), undef(), *undefined(), nil(), *null(), notNull()
  • Equality: equal(a[,b...]), notEqual(...), oneOf(arrayOrObject), *in(arrayOrObject)
  • Comparison: eq(n), lt(n), le(n), ge(n), gt(n), ne(n), min(n), max(n)
  • Numbers: number(), integer(), mod(x[,rem]), even(), odd()
  • Dates: date(), before([date]), after([date])
  • Arrays: array([validationForEachItem]), len(min,max), empty()
  • Strings: string(), len(min,max), blank(), notBlank()
  • Regexps: match(regex[,modifiers]), nomatch(regex[,modifiers])
  • Logic: and(test[,test...]), or(test[,test...]), not(test,message)
  • Utilities: nop(), fail([message]), message(msg), todo([test])
  • JSON: json(schema)

*: These function names are also JavaScript keywords. While Valid.undefined() works with a lot of interpreters, it doesn't work everywhere. Each keyword validation has a more compatible alternative that should be used instead: Valid.undef(), Valid.nil(), etc.


When a validation fails, check() returns a concise, positive message with the value implied at the front: "must be even", "can't be blank", etc. The messages are meant to be understandable by end users.

Concatenating the value and message is one obvioius use ("7 must be even"), but this style of wording is useful in other ways too. For instance, a web app can display the message to the right of the form element containing the error.

It's easy to supply your own error messages:

Valid.match(/-/).message("must contain a dash")

Because JSON validations need to return multiple errors, they return an object instead of a string. The error object has the same structure as the JSON except that arrays are converted into objects.

        Name: "is blank",
        Address: {
            State: "doesn't match /[A-Z][A-Z]/"

Extending Valid

To define your own validations, just end the chain with "define()" and add it to the root object:

    Valid.latitude  =;
    Valid.longitude =;
    Valid.integer().latitude().isValid(20);  // true!

You can also add validations that take parameters:

    Valid.mod10 = function(rem) { return this.mod(10,rem).message("must end in" + rem); }
    Valid.mod10(6).check(127);   // returns "must end in 6"

Or just rename them:

    Valid.every = Valid.and;
    Valid.any = Valid.or;

Here's a rogue's gallery of examples. Drop them in your code, customize as needed. You call them like any other validation: Valid.isNumeric().len(2).

    // TODO: test these!
    Validator.boolean =        Valid.type('boolean').message('must be a boolean').define();
    Validator.true    =        Valid.equal(true).message('must be true').define();
    Validator.false   =        Valid.equal(false).message('must be false').define();
    Validator.isAlpha =        Valid.match(/^[a-zA-Z]+$/).message("must be only letters").define();
    Validator.isAlphanumeric = Valid.match(/^[a-zA-Z0-9]+$/).message("must be letters or numbers").define();
    Validator.isNumeric =      Valid.match(/^-?[0-9]+$/).message("must be numeric").define();
    Validator.isLowercase =    Valid.match(/^[a-z]+$/).message("must be lower-case letters").define();
    Validator.isUppercase =    Valid.match(/^[A-Z]+$/).message("must be upper-case letters").define();
    Validator.noOutsideWS =    Valid.noMatch(/^\s+|\s+$/).message("must not have leading or trailing whitespace").define();
    Validator.noConsecutiveWS= Valid.noMatch(/\s\s/).message("must not have consecutive whitespace").define();
    Validator.noControlChars = Valid.noMatch(/[\x00-\x19\x7F]/).message("must not have control characters").define();
    Validator.saneString =     Valid.noOutsideWS().noConsecutiveWS().noControlChars().define();


On Node 0.4.x, if the console tries to print a Valid chain, you get this error:

> Valid.integer()
TypeError: Function.prototype.toString is not generic
    at Function.toString (native)
    at Array.toString (native)

It's a Node bug. 0.5.x does the correct thing and prints the chain:

> Valid.integer()
{ _queue: 
   [ { [Function: SimpleTest] data: [Object] },
     { [Function: SimpleTest] data: [Object] } ] }


  • The syntax is pretty sweet: check('abc').len(6,12).isEmail();
  • Only supports immediate use, can't declare validations.
  • Only meant to work inside node. Can't recurse over JSON.

  • Validates JSON using a declared schema.
  • Only supports static use, can't do immediate validations.
  • Produces unsatisfying error messages on deeply nested schemas.


Pain-free MIT.

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