Add Obtain Undefined Value With The Void Operator as a javascript til

javascript/obtain-undefined-value-with-the-void-operator.md

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+# Obtain Undefined Value With The Void Operator
+
+The [`void`
+operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/void)
+takes any expression, evaluates it, and then results in the `undefined` value.
+A common use of the `void` operator is to get the primitive `undefined` value
+in a consistent way.
+
+```javascript
+> void(0);
+undefined
+```
+
+This is handy for instances where you need to check if a value is `undefined`:
+
+```javascript
+function doSomething({ arg }) {
+  if (arg === void 0) {
+    throw new Error("arg is undefined 😱");
+  }
+
+  // ...
+};
+```