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javascript/snippets/is.md

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+---
+title: Check if value is of type
+type: snippet
+tags: [type]
+cover: coffee-phone-tray
+dateModified: 2020-10-20T23:02:01+03:00
+---
+
+Checks if the provided value is of the specified type.
+
+- Ensure the value is not `undefined` or `null` using `Array.prototype.includes()`.
+- Use `Object.prototype.constructor` to compare the constructor property on the value with `type` to check if the provided value is of the specified `type`.
+
+```js
+const is = (type, val) => ![, null].includes(val) && val.constructor === type;
+```
+
+```js
+is(Array, [1]); // true
+is(ArrayBuffer, new ArrayBuffer()); // true
+is(Map, new Map()); // true
+is(RegExp, /./g); // true
+is(Set, new Set()); // true
+is(WeakMap, new WeakMap()); // true
+is(WeakSet, new WeakSet()); // true
+is(String, ''); // true
+is(String, new String('')); // true
+is(Number, 1); // true
+is(Number, new Number(1)); // true
+is(Boolean, true); // true
+is(Boolean, new Boolean(true)); // true
+```