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    should is an expressive, readable, framework-agnostic assertion library. The main goals of this library are to be expressive and to be helpful. It keeps your test code clean, and your error messages helpful.

    By default (when you require('should')) should extends the Object.prototype with a single non-enumerable getter that allows you to express how that object should behave. It also returns itself when required with require.

    It is also possible to use should.js without getter (it will not even try to extend Object.prototype), just require('should/as-function'). Or if you already use version that auto add getter, you can call .noConflict function.

    Results of (something).should getter and should(something) in most situations are the same

    Upgrading instructions

    Please check wiki page for upgrading instructions.


    You can take look in FAQ.


    var should = require('should');
    var user = {
        name: 'tj'
      , pets: ['tobi', 'loki', 'jane', 'bandit']
'name', 'tj');'pets').with.lengthOf(4);
    // If the object was created with Object.create(null)
    // then it doesn't inherit `Object.prototype`, so it will not have `.should` getter
    // so you can do:
    should(user)'name', 'tj');
    // also you can test in that way for null's
    someAsyncTask(foo, function(err, result){

    To begin

    1. Install it:

      $ npm install should --save-dev
    2. Require it and use:

      var should = require('should');
      var should = require('should/as-function');
    3. For TypeScript users:

    import * as should from 'should';

    In browser

    Well, even when browsers by complaints of authors have 100% es5 support, it does not mean it has no bugs. Please see wiki for known bugs.

    If you want to use should in browser, use the should.js file in the root of this repository, or build it yourself. To build a fresh version:

    $ npm install
    $ npm run browser

    The script is exported to window.should:


    You can easy install it with npm or bower:

    npm install should -D
    # or 
    bower install shouldjs/should.js

    API docs

    Actual api docs generated by jsdoc comments and available at

    Usage examples

    Please look on usage in examples


    .not negates the current assertion.


    .any allow for assertions with multiple parameters to assert any of the parameters (but not all). This is similar to the native JavaScript array.some.


    chaining assertions

    Every assertion will return a should.js-wrapped Object, so assertions can be chained. To help chained assertions read more clearly, you can use the following helpers anywhere in your chain: .an, .of, .a, .and, .be, .have, .with, .is, .which. Use them for better readability; they do nothing at all. For example:'name', 'tj');;

    Almost all assertions return the same object - so you can easy chain them. But some (eg: .length and .property) move the assertion object to a property value, so be careful.

    Adding own assertions

    Adding own assertion is pretty easy. You need to call should.Assertion.add function. It accept 2 arguments:

    1. name of assertion method (string)
    2. assertion function (function)

    What assertion function should do. It should check only positive case. should will handle .not itself. this in assertion function will be instance of should.Assertion and you must define in any way this.params object in your assertion function call before assertion check happen.

    params object can contain several fields:

    • operator - it is string which describe your assertion
    • actual it is actual value, you can assume it is your own this.obj if you need to define you own
    • expected it is any value that expected to be matched this.obj

    You can assume its usage in generating AssertionError message like: expected obj? || this.obj not? operator expected?

    In should sources appeared 2 kinds of usage of this method.

    First not preferred and used only for shortcuts to other assertions, e.g how defined:

    Assertion.add('true', function() {;

    There you can see that assertion function do not define own this.params and instead call within the same assertion .exactly that will fill this.params. You should use this way very carefully, but you can use it.

    Second way preferred and i assume you will use it instead of first.

    Assertion.add('true', function() {
        this.params = { operator: 'to be true', expected: true };

    in this case this.params defined and then used new assertion context (because called .should). Internally this way does not create any edge cases as first.

    Assertion.add('asset', function() {
        this.params = { operator: 'to be asset' };
    > ({ id: '10' });
    AssertionError: expected { id: '10' } to be asset
        expected '10' to be a number
    > ({ id: 10 });
    AssertionError: expected { id: 10 } to be asset
        expected { id: 10 } to have property path

    Additional projects

    • should-sinon - adds additional assertions for sinon.js
    • should-immutable - extends different parts of should.js to make immutable.js first-class citizen in should.js
    • should-http - adds small assertions for assertion on http responses for node only
    • should-jq - assertions for jq (need maintainer)
    • karma-should - make more or less easy to work karma with should.js
    • should-spies - small and dirty simple zero dependencies spies


    Actual list of contributors if you want to show it your friends.

    To run the tests for should simply run:

    $ npm test

    See also CONTRIBUTING.


    Yes, yes it does, with a single getter should, and no it won't break your code, because it does this properly with a non-enumerable property.

    Also it is possible use it without extension. Just use require('should/as-function') everywhere.


    MIT. See LICENSE for details.


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