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javascript/snippets/check-prop.md

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+---
+title: Check property
+type: snippet
+tags: [function,object]
+cover: white-tablet-2
+dateModified: 2020-11-01T20:50:57+02:00
+---
+
+Creates a function that will invoke a predicate function for the specified property on a given object.
+
+- Return a curried function, that will invoke `predicate` for the specified `prop` on `obj` and return a boolean.
+
+```js
+const checkProp = (predicate, prop) => obj => !!predicate(obj[prop]);
+```
+
+```js
+const lengthIs4 = checkProp(l => l === 4, 'length');
+lengthIs4([]); // false
+lengthIs4([1, 2, 3, 4]); // true
+lengthIs4(new Set([1, 2, 3, 4])); // false (Set uses Size, not length)
+
+const session = { user: {} };
+const validUserSession = checkProp(u => u.active && !u.disabled, 'user');
+
+validUserSession(session); // false
+
+session.user.active = true;
+validUserSession(session); // true
+
+const noLength = checkProp(l => l === undefined, 'length');
+noLength([]); // false
+noLength({}); // true
+noLength(new Set()); // true
+```