Add The Comma Operator as a javascript til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_736 TILs and counting..._
+_737 TILs and counting..._
 
 ---
 
@@ -279,6 +279,7 @@ _736 TILs and counting..._
 - [Spread The Rest With ES6](javascript/spread-the-rest-with-es6.md)
 - [String Interpolation With Template Literals](javascript/string-interpolation-with-template-literals.md)
 - [Test Coverage Stats With Jest](javascript/test-coverage-stats-with-jest.md)
+- [The Comma Operator](javascript/the-comma-operator.md)
 - [Throttling A Function Call](javascript/throttling-a-function-call.md)
 - [Timing Processes](javascript/timing-processes.md)
 - [Transforming ES6 and JSX With Babel 6](javascript/transforming-es6-and-jsx-with-babel-6.md)

javascript/the-comma-operator.md

@@ -0,0 +1,18 @@
+# The Comma Operator
+
+I was surprised to see the result of this line of code:
+
+```javascript
+const what = (1,2,3,4);
+console.log(what); //=> 4
+```
+
+I asked around on
+[twitter](https://twitter.com/jbrancha/status/1084936559323951105) and
+learned that the syntax construct at play here is the [comma
+operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator).
+
+> The comma operator evaluates each of its operands (from left to right) and
+> returns the value of the last operand.
+
+And that is why `what` gets bound to `4`.