33 lines
935 B
Markdown
33 lines
935 B
Markdown
---
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title: checkProp
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tags: function,object,beginner
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---
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Given a `predicate` function and a `prop` string, this curried function will then take an `object` to inspect by calling the property and passing it to the predicate.
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Summon `prop` on `obj`, pass it to a provided `predicate` function and return a masked boolean.
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```js
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const checkProp = (predicate, prop) => obj => !!predicate(obj[prop]);
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```
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```js
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const lengthIs4 = checkProp(l => l === 4, 'length');
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lengthIs4([]); // false
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lengthIs4([1, 2, 3, 4]); // true
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lengthIs4(new Set([1, 2, 3, 4])); // false (Set uses Size, not length)
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const session = { user: {} };
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const validUserSession = checkProp(u => u.active && !u.disabled, 'user');
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validUserSession(session); // false
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session.user.active = true;
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validUserSession(session); // true
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const noLength = checkProp(l => l === undefined, 'length');
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noLength([]); // false
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noLength({}); // true
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noLength(new Set()); // true
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```
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