Add Sleep For A Bit In Async Code as a JavaScript til

Author: jbranchaud

README.md

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@@ -413,6 +413,7 @@ _1159 TILs and counting..._
 - [Resolve And Pass Multiple Values From A Then](javascript/resolve-and-pass-multiple-values-from-a-then.md)
 - [Running ES6 Specs With Mocha](javascript/running-es6-specs-with-mocha.md)
 - [Scoping Variables With A Block Statement](javascript/scoping-variables-with-a-block-statement.md)
+- [Sleep For A Bit In Async Code](javascript/sleep-for-a-bit-in-async-code.md)
 - [Sorting Arrays Of Objects With Lodash](javascript/sorting-arrays-of-objects-with-lodash.md)
 - [Splat Arguments To A Function](javascript/splat-arguments-to-a-function.md)
 - [Spread The Rest With ES6](javascript/spread-the-rest-with-es6.md)

javascript/sleep-for-a-bit-in-async-code.md

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+# Sleep For A Bit In Async Code
+
+A `sleep` utility function can be useful in a variety of situations. From
+testing and debugging to simulating a delay in development.
+
+Here is what that function can look like in its simplest form:
+
+```javascript
+function sleep(time) {
+  return new Promise((resolve) => {
+    setTimeout(resolve, time)
+  })
+}
+```
+
+This function returns a promise that will resolve after the given number of
+milliseconds.
+
+As an example of how to use it, here is how we can simulate a delay in a fake
+fetch function.
+
+```javascript
+async function fakeUserFetch(userId) {
+  # add half a second of "network" latency
+  await sleep(500)
+
+  const fakeResponse = {
+    id: userId,
+    email: "fake-email@example.com"
+  }
+
+  return Promise.resolve(fakeResponse)
+}
+```