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78 lines
2.5 KiB
78 lines
2.5 KiB
"use strict"
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// global key for user preferred registration
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var REGISTRATION_KEY = '@@any-promise/REGISTRATION',
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// Prior registration (preferred or detected)
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registered = null
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/**
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* Registers the given implementation. An implementation must
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* be registered prior to any call to `require("any-promise")`,
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* typically on application load.
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*
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* If called with no arguments, will return registration in
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* following priority:
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*
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* For Node.js:
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*
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* 1. Previous registration
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* 2. global.Promise if node.js version >= 0.12
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* 3. Auto detected promise based on first sucessful require of
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* known promise libraries. Note this is a last resort, as the
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* loaded library is non-deterministic. node.js >= 0.12 will
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* always use global.Promise over this priority list.
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* 4. Throws error.
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*
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* For Browser:
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*
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* 1. Previous registration
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* 2. window.Promise
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* 3. Throws error.
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*
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* Options:
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*
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* Promise: Desired Promise constructor
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* global: Boolean - Should the registration be cached in a global variable to
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* allow cross dependency/bundle registration? (default true)
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*/
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module.exports = function(root, loadImplementation){
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return function register(implementation, opts){
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implementation = implementation || null
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opts = opts || {}
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// global registration unless explicitly {global: false} in options (default true)
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var registerGlobal = opts.global !== false;
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// load any previous global registration
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if(registered === null && registerGlobal){
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registered = root[REGISTRATION_KEY] || null
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}
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if(registered !== null
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&& implementation !== null
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&& registered.implementation !== implementation){
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// Throw error if attempting to redefine implementation
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throw new Error('any-promise already defined as "'+registered.implementation+
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'". You can only register an implementation before the first '+
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' call to require("any-promise") and an implementation cannot be changed')
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}
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if(registered === null){
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// use provided implementation
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if(implementation !== null && typeof opts.Promise !== 'undefined'){
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registered = {
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Promise: opts.Promise,
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implementation: implementation
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}
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} else {
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// require implementation if implementation is specified but not provided
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registered = loadImplementation(implementation)
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}
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if(registerGlobal){
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// register preference globally in case multiple installations
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root[REGISTRATION_KEY] = registered
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}
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}
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return registered
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}
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}
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