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Strategy implements a strategy for selecting the correct transport based on a given set of restrictions. The module should work for every transport that is created using the transport-layer module.


As this module can be used with node.js and browserify it's released in the npm registry and can be installed using:

npm install --save recovery

The --save tells npm to automatically add the installed version to your package.json if one exists.


In all API examples we assume that you've already required and initialized a new Strategy instance using:

'use strict';
var Strategy = require('strategy')
  , Policy = Strategy.Policy
  , strategy = new Strategy();

The Strategy constructor allows one option argument and that is a list of pre-generated Policy instances (don't worry, you can always add more later). A Policy instance accepts the following arguments:

  1. Name of the policy, It can be omitted if you want to use the .name from the Transport's prototype.
  2. Transport Layer transport.
  3. Additional options that should be used for constructing a new instance.
var TransportLayer = require('transport-layer')
  , WebSockets
  , attempt;
WebSockets = TransportLayer.extend({
  name: 'websockets'
}, {
  readyState: 'complete',
  crossdomain: true,
  readable: true,
  writable: true
attempt = new Policy(WebSockets, { /* options * /});
// or:
attempt = new Policy('WebSockets', WebSockets, { /* options */});

Now that you've got some transports created you can assign them supply them to Strategy:

strategy = new Strategy([attempt /*, .. and more .. */]);


Add new Policy to the strategy. If you don't supply a policy instance as first argument we will automatically create a new one. The following arguments are accepted by this method:

  1. Name of the policy your about to push. If this is an Policy instance, we will not create a new one and you can safely ignore all other arguments.
  2. Transport that belongs to this policy.
  3. Options for the transport.
.push('websockets', WebSockets, { foo: 'bar' })
.push(TransportLayer.extend({ 'iframes' }, { readable: true }));

Select a new policy from the strategy. To find a suitable policy we need to know some specifics first. These specifics can be:

  • crossdomain: The transport should work cross domain.
  • not: The transport should not be in the given list, should be an object where the keys are lowercase names of the policies we should exclude.
  • available: The transport should be.
  • readable: The transport should be readable.
  • writable: The transport should be readable.
  • id: The id we should start at.

The method requires 2 arguments:

  • Configuration object with one or multiple properties mentioned.
  • Completion callback which follows an error first callback pattern.{
  crossdomain: true,
  not: { jsonp: true, htmlfile: true },
  readable: true,
  available: 'complete'
}, function (err, policy) {
  console.log(;       // Name of the policy, in lowercase.
  console.log(policy.transport);  // Reference to transport.
  console.log(policy.options);    // Additional configuration.


Completely destroy the strategy instance.




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npm i strategy

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