Use explicit default value

snippets/standard-deviation.md

@@ -6,7 +6,7 @@ of the values to determine the standard deviation of an array of numbers.
 Since there are two types of standard deviation, population and sample, you can use a flag to switch to population (sample is default).
 
 ```js
-const standardDeviation = (arr, usePopulation) => {
+const standardDeviation = (arr, usePopulation = false) => {
   const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
   return Math.sqrt(
     arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])