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snippets/js/s/functions.md

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+---
+title: Function property names
+type: snippet
+language: javascript
+tags: [object,function]
+cover: palm-tree-house
+dateModified: 2020-10-20T11:21:07+03:00
+---
+
+Gets an array of function property names from own (and optionally inherited) enumerable properties of an object.
+
+- Use `Object.keys()` to iterate over the object's own properties.
+- If `inherited` is `true`, use `Object.getPrototypeOf()` to also get the object's inherited properties.
+- Use `Array.prototype.filter()` to keep only those properties that are functions.
+- Omit the second argument, `inherited`, to not include inherited properties by default.
+
+```js
+const functions = (obj, inherited = false) =>
+  (inherited
+    ? [...Object.keys(obj), ...Object.keys(Object.getPrototypeOf(obj))]
+    : Object.keys(obj)
+  ).filter(key => typeof obj[key] === 'function');
+```
+
+```js
+function Foo() {
+  this.a = () => 1;
+  this.b = () => 2;
+}
+Foo.prototype.c = () => 3;
+functions(new Foo()); // ['a', 'b']
+functions(new Foo(), true); // ['a', 'b', 'c']
+```