Merge pull request #455 from atomiks/once

[ADD `once.md`] once

snippets/once.md

@@ -0,0 +1,18 @@
+### once
+
+Ensures a function is called only once.
+
+Utilizing a closure, use a flag, `called`, and set it to `true` once the function is called for the first time, preventing it from being called again. 
+Allow the function to be supplied with an arbitrary number of arguments using the spread (`...`) operator.
+
+```js
+const once = fn => (called => (...args) => !called ? (called = true, fn(...args)) : undefined)()
+```
+
+```js
+const startApp = event => {
+  // initializes the app
+  console.log(event); // access to any arguments supplied
+};
+document.addEventListener('click', once(startApp)); // only runs `startApp` once upon click
+```

tag_database

@@ -103,6 +103,7 @@ negate:logic
 nthElement:array
 objectFromPairs:object
 objectToPairs:object
+once:function
 onUserInputChange:browser
 orderBy:object
 palindrome:string