--- /dev/null
+var wrappy = require('wrappy')
+module.exports = wrappy(once)
+
+once.proto = once(function () {
+ Object.defineProperty(Function.prototype, 'once', {
+ value: function () {
+ return once(this)
+ },
+ configurable: true
+ })
+})
+
+function once (fn) {
+ var f = function () {
+ if (f.called) return f.value
+ f.called = true
+ return f.value = fn.apply(this, arguments)
+ }
+ f.called = false
+ return f
+}