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Diffstat (limited to 'tools/node_modules/eslint/lib/util/safe-emitter.js')
-rw-r--r-- | tools/node_modules/eslint/lib/util/safe-emitter.js | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/util/safe-emitter.js b/tools/node_modules/eslint/lib/util/safe-emitter.js new file mode 100644 index 0000000000..2fa373cb96 --- /dev/null +++ b/tools/node_modules/eslint/lib/util/safe-emitter.js @@ -0,0 +1,54 @@ +/** + * @fileoverview A variant of EventEmitter which does not give listeners information about each other + * @author Teddy Katz + */ + +"use strict"; + +//------------------------------------------------------------------------------ +// Typedefs +//------------------------------------------------------------------------------ + +/** + * An event emitter + * @typedef {Object} SafeEmitter + * @property {function(eventName: string, listenerFunc: Function): void} on Adds a listener for a given event name + * @property {function(eventName: string, arg1?: any, arg2?: any, arg3?: any)} emit Emits an event with a given name. + * This calls all the listeners that were listening for that name, with `arg1`, `arg2`, and `arg3` as arguments. + * @property {function(): string[]} eventNames Gets the list of event names that have registered listeners. + */ + +/** + * Creates an object which can listen for and emit events. + * This is similar to the EventEmitter API in Node's standard library, but it has a few differences. + * The goal is to allow multiple modules to attach arbitrary listeners to the same emitter, without + * letting the modules know about each other at all. + * 1. It has no special keys like `error` and `newListener`, which would allow modules to detect when + * another module throws an error or registers a listener. + * 2. It calls listener functions without any `this` value. (`EventEmitter` calls listeners with a + * `this` value of the emitter instance, which would give listeners access to other listeners.) + * 3. Events can be emitted with at most 3 arguments. (For example: when using `emitter.emit('foo', a, b, c)`, + * the arguments `a`, `b`, and `c` will be passed to the listener functions.) + * @returns {SafeEmitter} An emitter + */ +module.exports = () => { + const listeners = Object.create(null); + + return Object.freeze({ + on(eventName, listener) { + if (eventName in listeners) { + listeners[eventName].push(listener); + } else { + listeners[eventName] = [listener]; + } + }, + emit(eventName, a, b, c) { + if (eventName in listeners) { + listeners[eventName].forEach(listener => listener(a, b, c)); + } + }, + eventNames() { + return Object.keys(listeners); + } + }); +}; |