Add Scoping Variables With A Block Statement as a javascript til

javascript/scoping-variables-with-a-block-statement.md

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+# Scoping Variables With A Block Statement
+
+A solid way to keep code readable and easy to understand is to ditch the
+terse one-liners in favor of breaking things up across multiple lines and
+using self-documenting variable names. This isn't all good though. Each new
+variable that is defined is a handle on some data that can be misused later
+in the syntax scope.
+
+JavaScript has a nice way of being clear about the scope of certain
+variables:
+
+```javascript
+let parsedDate;
+{
+  let [month, day, year] = input.split('-');
+  parsedDate = new Date(year, month, day);
+}
+
+// do something with parsedDate
+```
+
+The `month`, `day`, and `year` variables are scoped to the `{ ... }` which
+is a [block
+statement](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/block).
+This helps communicate and enforce that those variables are only to be used
+in that very specific context. Other developers and our future selves won't
+be able to erroneously use those variables.
+
+Of course, breaking out a function is another way of accomplishing this.
+Sequestering code in a different part of the file is not always the best
+answer though. Sometimes you want it locally fenced off. For those times,
+use a block statement.