node_modules/events/tests/listeners-side-effects.js

// Copyright Joyent, Inc. and other Node contributors.
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var assert = require('assert');
var EventEmitter = require('../').EventEmitter;

var e = new EventEmitter;
var fl;  // foo listeners

fl = e.listeners('foo');
assert(Array.isArray(fl));
assert(fl.length === 0);
assert.deepEqual(e._events, {});

e.on('foo', assert.fail);
fl = e.listeners('foo');
assert(e._events.foo === assert.fail);
assert(Array.isArray(fl));
assert(fl.length === 1);
assert(fl[0] === assert.fail);

e.listeners('bar');
assert(!e._events.hasOwnProperty('bar'));

e.on('foo', assert.ok);
fl = e.listeners('foo');

assert(Array.isArray(e._events.foo));
assert(e._events.foo.length === 2);
assert(e._events.foo[0] === assert.fail);
assert(e._events.foo[1] === assert.ok);

assert(Array.isArray(fl));
assert(fl.length === 2);
assert(fl[0] === assert.fail);
assert(fl[1] === assert.ok);