Auto-install httpserver npm module

Author: bkoelman

docs/README.md

@@ -1,13 +1,9 @@
 # Intro
-Documentation for JsonApiDotNetCore is produced using [DocFX](https://dotnet.github.io/docfx/) from several files in this directory.
+Documentation for JsonApiDotNetCore is produced using [docfx](https://dotnet.github.io/docfx/) from several files in this directory.
 In addition, the example request/response pairs are generated by executing `curl` commands against the GettingStarted project.
 
 # Installation
-Run the following command once to setup your system:
-
-```
-npm install -g httpserver
-```
+You need to have 'npm' installed. Download Node.js from https://nodejs.org/.
 
 # Running
 The next command regenerates the documentation website and opens it in your default browser:

docs/build-dev.ps1

@@ -1,9 +1,6 @@
 #Requires -Version 7.0
 
 # This script builds the documentation website, starts a web server and opens the site in your browser. Intended for local development.
-# It is assumed that you have already installed httpserver.
-# If that's not the case, run the next command:
-#   npm install -g httpserver
 
 param(
     # Specify -NoBuild to skip code build and examples generation. This runs faster, so handy when only editing Markdown files.
@@ -16,6 +13,21 @@ function VerifySuccessExitCode {
     }
 }
 
+function EnsureHttpServerIsInstalled {
+    if ((Get-Command "npm" -ErrorAction SilentlyContinue) -eq $null) {
+        throw "Unable to find npm in your PATH. please install Node.js first."
+    }
+
+    npm list --depth 1 --global httpserver >$null
+
+    if ($LastExitCode -eq 1) {
+        npm install -g httpserver
+    }
+}
+
+EnsureHttpServerIsInstalled
+VerifySuccessExitCode
+
 if (-Not $NoBuild -Or -Not (Test-Path -Path _site)) {
     Remove-Item _site -Recurse -ErrorAction Ignore