codetags

> A simple feature toggle utility

What is codetags?

codetags is a simple feature toggle utility for javascript/nodejs. Developers could use this library to prepare new features and switch the features by using environment variables.

How does it work?

!Architecture

$3

A default codetags instance can be retrieved simply by a require call:

``shell
const codetags = require('codetags');
`

We can create multiple codetags's instance with newInstance or getInstance methods. Call to both will create a codetags instance, but the getInstance creates a new instance only if it has not existed before.

`javascript
const codetags = require('codetags');

const space1 = codetags.getInstance('main', {
namespace: 'maincode'
});
const space2 = codetags.newInstance('test', {
namespace: 'testcode'
});

// ...

const space3 = codetags.getInstance('main', {
namespace: 'maincode'
});
console.log(space3 === space1); // true
const space4 = codetags.newInstance('test', {
namespace: 'testcode'
});
console.log(space4 === space2); // false
`

$3

Default tags can be initialized by register() method:

`javascript
codetags_instance.register(an_array_of_tag_descriptors);
`

For example:

`javascript
codetags.register(['a-simple-tag']);
`

similar to:

`javascript
codetags.register([
{
name: 'a-simple-tag',
enabled: true
}
]);
`

More complex example:

`javascript
codetags.register([
'foo',
{
name: 'bar'
},
{
name: 'nil',
enabled: false
}
]);
`

$3

`javascript
const codetags = require('codetags');

// ...

if (codetags.isActive('foo')) {
// do something
}

if (tryit.isActive(['foo', 'bar'])) {
// do other things
}
`

$3

Declare environment variables:

`shell
export CODETAGS_INCLUDED_TAGS=nil,foo
export CODETAGS_EXCLUDED_TAGS=bar
`

Start node program:

`shell
node index.js
`

Methods

$3

The kwargs composes of following fields:

* namespace - a customized namespace.
* INCLUDED_TAGS - a customized label for included tags environment variable name (default: INCLUDED_TAGS).
* EXCLUDED_TAGS - a customized label for excluded tags environment variable name (default: EXCLUDED_TAGS).
* version - the current package version.

This method returns the codetags instance itself.

$3

Method register() is used to define the default declaredTags collection.

The argument descriptors is an array of descriptor objects which of each describing a string label together with the range of versions that will be applied.

`javascript
const descriptor1 = {
name: 'tag-1',
plan: {
minBound: '0.1.3',
enabled: true
}
}

const descriptor2 = {
name: 'tag-2',
plan: {
maxBound: '0.2.7',
enabled: false
}
}

const descriptor3 = {
name: 'tag-3',
plan: {
minBound: '0.1.2',
maxBound: '0.2.8',
enabled: false
}
}

const descriptors = [ descriptor1, descriptor2, descriptor3 ];

codetags.register(descriptors);
`

This method returns the codetags instance itself.

$3

Method isActive() evaluates tags filter expressions (named tagexp) based on three collections of tags (declaredTags, includedTags, excludedTags) to determine whether it is accepted or denied. An expression of tags is composed by string labels, arrays, hashmaps and conditional operators ($all, $any, $not).

#### tagexp is a single string

Syntax:

`javascript
const tagexp = 'tagexp-is-a-string';
if (codetags.isActive(tagexp)) {
// do something
}
`

Function call codetags.isActive(tagexp) returns true when:

* excludedTags does not contain tagexp-is-a-string;
* at least one of includedTags and declaredTags contains tagexp-is-a-string.

#### tagexp is an array of sub-tagexps

Syntax:

`javascript
const tagexp = [subtagexp_1, subtagexp_2, subtagexp_3];
if (codetags.isActive(tagexp)) {
// do something
}
`

Function call codetags.isActive(tagexp) returns true if all of sub-tagexp in the array must satisfy the function codetags.isActive (i.e. codetags.isActive(subtagexp_i)) return true for any i from 1 to 3).

#### tagexp is a conditional expression

Syntax:

`javascript
const tagexp = {
$all: [
{
$not: subtagexp_0,
$any: [ subtagexp_1, subtagexp_2, subtagexp_3 ]
},
{
$any: [ subtagexp_4, subtagexp_5 ]
}
]
};
if (codetags.isActive(tagexp)) {
// do something
}
`

Function call codetags.isActive(tagexp) returns true if the sub-tagexps are satisfied the following constraints:

* codetags.isActive(subtagexp_0) returns false;
* one of codetags.isActive(subtagexp_i) returns true (with i from 1 to 3);
* one of codetags.isActive(subtagexp_j) returns true (with j is 4 or 5);

#### arguments is a sequence of tagexps

Syntax:

`javascript
codetags.isActive(tagexp1, tagexp2, tagexp3);
`

The above function call will return true if there is at least one of tagexp arguments satisfies the function codetags.isActive. It is equivalent to the following expression:

`javascript
codetags.isActive(tagexp1) || codetags.isActive(tagexp2) || codetags.isActive(tagexp3)
`

$3

Method clearCache() clears the cached values of tags filtering result as well as the cached values of environment variables. This method returns the codetags instance itself.

$3

Method reset() invokes the method clearCache() as well as clears the values of declaredTags collection that has been defined by register() method. This method also returns the codetags instance itself.

$3

Method newInstance() creates a new instance in each time it is called and assigns name to this instance. The name value is associated with the latest instance. If you want to retrieve the already created instance, using getInstance instead. The arguments can be:

* name: a string as name (using in getInstance() to retrieve the instance);
* opts: an option object that is similar to which in initialize();

This method returns the created instance.

$3

Method getInstance() returns the instance associated to name or creates a new instance when it has not existed before. Its arguments are the same as the method newInstance().

Examples

$3

Register feature tags:

`javascript
// file: bootstrap.js
const codetags = require('codetags');

codetags.register([
{
name: 'replace-console-log-with-winston',
enabled: false
},
{
name: 'moving-from-mongodb-to-couchbase',
enabled: true
},
]);
`

Check the state of tags:

`javascript
// file: index.js
require('./bootstrap.js');
const codetags = require('codetags');

// ...

if (codetags.isActive('replace-console-log-with-winston')) {
// be disabled by default
winston.log('debug', 'Hello world from winston');
} else {
console.log('Hello world from console.log');
}
`

Change state of tags with environment variables:

`shell
export CODETAGS_INCLUDED_TAGS=replace-console-log-with-winston
export CODETAGS_EXCLUDED_TAGS=moving-from-mongodb-to-couchbase
node index.js
`

$3

Create multiple codetags instances:

`javascript
// file: bootstrap.js
const codetags = require('codetags');

// features for trunk branch
const trunk = codetags.newInstance('trunk', {
namespace: 'my_mission'
});

trunk.register([
{
name: 'replace-console-log-with-winston',
enabled: false
},
{
name: 'moving-from-mongodb-to-couchbase',
enabled: true
},
]);

// features for trial branch
const trial = codetags.newInstance('trial', {
namespace: 'my_passion'
});

trial.register(['foo', 'bar']);
`

Make conditional flow:

`javascript
// file: index.js
require('./bootstrap.js');
const codetags = require('codetags');
const trunk = codetags.getInstance('trunk');
const tryit = codetags.getInstance('trial');

// ...

if (trunk.isActive('replace-console-log-with-winston')) {
// be disabled by default
winston.log('debug', 'Hello world from winston');
} else {
console.log('Hello world from console.log');
}

// ...

if (tryit.isActive('foo')) {
// do something here
}

if (tryit.isActive(['foo', 'bar'])) {
// and here
}

if (tryit.isActive('foo', 'bar')) {
// and here
}
`

Change state of tags with environment variables:

`shell
export MY_MISSION_INCLUDED_TAGS=replace-console-log-with-winston
export MY_PASSION_EXCLUDED_TAGS=foo,bar
node index.js
``

License

MIT

See LICENSE to see the full text.