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A very simple EventEmitter in pure JavaScript (suitable for both node.js and browsers).
/* Polyfill indexOf. */
var indexOf;
if (typeof Array.prototype.indexOf === 'function') {
indexOf = function (haystack, needle) {
return haystack.indexOf(needle);
};
} else {
indexOf = function (haystack, needle) {
var i = 0, length = haystack.length, idx = -1, found = false;
while (i < length && !found) {
if (haystack[i] === needle) {
idx = i;
found = true;
}
i++;
}
return idx;
};
};
/* Polyfill EventEmitter. */
var EventEmitter = function () {
this.events = {};
};
EventEmitter.prototype.on = function (event, listener) {
if (typeof this.events[event] !== 'object') {
this.events[event] = [];
}
this.events[event].push(listener);
};
EventEmitter.prototype.removeListener = function (event, listener) {
var idx;
if (typeof this.events[event] === 'object') {
idx = indexOf(this.events[event], listener);
if (idx > -1) {
this.events[event].splice(idx, 1);
}
}
};
EventEmitter.prototype.emit = function (event) {
var i, listeners, length, args = [].slice.call(arguments, 1);
if (typeof this.events[event] === 'object') {
listeners = this.events[event].slice();
length = listeners.length;
for (i = 0; i < length; i++) {
listeners[i].apply(this, args);
}
}
};
EventEmitter.prototype.once = function (event, listener) {
this.on(event, function g () {
this.removeListener(event, g);
listener.apply(this, arguments);
});
};
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