Use const

snippets/run-promises-in-series.md

@@ -3,7 +3,7 @@
 Run an array of promises in series using `Array.reduce()` by creating a promise chain, where each promise returns the next promise when resolved.
 
 ```js
-var series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
-// var delay = (d) => new Promise(r => setTimeout(r, d))
+const series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
+// const delay = (d) => new Promise(r => setTimeout(r, d))
 // series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to complete
 ```