30 lines
818 B
Markdown
30 lines
818 B
Markdown
---
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title: is
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tags: type,array,intermediate
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---
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Checks if the provided value is of the specified type.
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- Ensure the value is not `undefined` or `null` using `Array.prototype.includes()`.
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- Compare the `constructor` property on the value with `type` to check if the provided value is of the specified `type`.
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```js
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const is = (type, val) => ![, null].includes(val) && val.constructor === type;
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```
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```js
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is(Array, [1]); // true
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is(ArrayBuffer, new ArrayBuffer()); // true
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is(Map, new Map()); // true
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is(RegExp, /./g); // true
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is(Set, new Set()); // true
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is(WeakMap, new WeakMap()); // true
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is(WeakSet, new WeakSet()); // true
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is(String, ''); // true
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is(String, new String('')); // true
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is(Number, 1); // true
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is(Number, new Number(1)); // true
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is(Boolean, true); // true
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is(Boolean, new Boolean(true)); // true
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```
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