Verify that the local Node.js version is 8.3.0+ (for NPM 5) before using it to build the static resources

Verify that the local Node.js version is 9.2.0+ before using it to build
the static resources

Blazor.sln

@@ -32,6 +32,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Blazor.DevHost",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "BlazorStandalone", "samples\BlazorStandalone\BlazorStandalone.csproj", "{754BBACA-E05B-4DAE-ACFC-1B3B429AE43F}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Microsoft.Blazor.BuildTools", "src\Microsoft.Blazor.BuildTools\Microsoft.Blazor.BuildTools.csproj", "{BB34336F-E68E-4411-9805-CAAA919F5EA1}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -74,6 +76,10 @@ Global
 		{754BBACA-E05B-4DAE-ACFC-1B3B429AE43F}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{754BBACA-E05B-4DAE-ACFC-1B3B429AE43F}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{754BBACA-E05B-4DAE-ACFC-1B3B429AE43F}.Release|Any CPU.Build.0 = Release|Any CPU
+		{BB34336F-E68E-4411-9805-CAAA919F5EA1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{BB34336F-E68E-4411-9805-CAAA919F5EA1}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{BB34336F-E68E-4411-9805-CAAA919F5EA1}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{BB34336F-E68E-4411-9805-CAAA919F5EA1}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -89,6 +95,7 @@ Global
 		{58D2DF2E-4181-4B16-9C69-A3F3EDB89B28} = {B867E038-B3CE-43E3-9292-61568C46CDEB}
 		{EE690312-2353-4DD0-9250-EE5EDAC6D4F7} = {B867E038-B3CE-43E3-9292-61568C46CDEB}
 		{754BBACA-E05B-4DAE-ACFC-1B3B429AE43F} = {F5FDD4E5-6A52-4A86-BE5E-5E42CB1DC8DA}
+		{BB34336F-E68E-4411-9805-CAAA919F5EA1} = {B867E038-B3CE-43E3-9292-61568C46CDEB}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {504DA352-6788-4DC0-8705-82167E72A4D3}

src/Microsoft.Blazor.Browser/Microsoft.Blazor.Browser.csproj

@@ -15,16 +15,18 @@
     <WebpackInputs Include="**\*.ts" Exclude="node_modules\**" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\Microsoft.Blazor.BuildTools\Microsoft.Blazor.BuildTools.csproj" ReferenceOutputAssembly="false" />
+  </ItemGroup>
+  <Import Project="..\Microsoft.Blazor.BuildTools\local.props" />
+
   <Target Name="EnsureNpmRestored" Condition="!Exists('node_modules')">
-    <Exec Command="node --version" ContinueOnError="true">
+    <Exec Command="$(BlazorBuildTools) checknodejs -v 8.3.0" />
-      <Output TaskParameter="ExitCode" PropertyName="ErrorCode" />
-    </Exec>
-    <Error Condition="'$(ErrorCode)' != '0'" Text="Node.js is required to build and run this project. To continue, please install Node.js from https://nodejs.org/, and then restart your command prompt or IDE." />
     <Message Importance="high" Text="Restoring dependencies using 'npm'. This may take several minutes..." />
     <Exec Command="npm install" />
   </Target>
 
-  <Target Name="RunWebpack" BeforeTargets="PreBuildEvent" Inputs="@(WebpackInputs)" Outputs="dist\blazor.js" DependsOnTargets="EnsureNpmRestored">
+  <Target Name="RunWebpack" AfterTargets="ResolveReferences" Inputs="@(WebpackInputs)" Outputs="dist\blazor.js" DependsOnTargets="EnsureNpmRestored">
     <RemoveDir Directories="dist" />
     <Exec Command="npm run build" />
     <ItemGroup>

src/Microsoft.Blazor.BuildTools/Cli/CheckNodeJsInstalled.cs

@@ -0,0 +1,93 @@
+using Microsoft.Extensions.CommandLineUtils;
+using System;
+using System.Diagnostics;
+using System.Text.RegularExpressions;
+
+namespace Microsoft.Blazor.BuildTools.Cli
+{
+    class CheckNodeJsInstalled
+    {
+        private static Regex NodeVersionRegex = new Regex(@"^v(\d+\.\d+\.\d+)");
+
+        public static void Command(CommandLineApplication command)
+        {
+            command.Description = "Asserts that Node.js is installed.";
+            command.HelpOption("-?|-h|--help");
+
+            var minVersionOption = command.Option(
+                "-v|--version",
+                "Specifies a minimum acceptable version of Node.js.",
+                CommandOptionType.SingleValue);
+
+            command.OnExecute(() =>
+            {
+                var foundNodeVersion = GetInstalledNodeVersion();
+                if (foundNodeVersion == null)
+                {
+                    return 1;
+                }
+
+                if (minVersionOption.HasValue())
+                {
+                    var minVersion = new Version(minVersionOption.Value());
+                    if (foundNodeVersion < minVersion)
+                    {
+                        Console.WriteLine($"ERROR: The installed version of Node.js is too old. Required version: {minVersion}; Found version: {foundNodeVersion}.");
+                        return 1;
+                    }
+                }
+
+                Console.WriteLine($"Found Node.js version {foundNodeVersion}");
+                return 0;
+            });
+        }
+
+        private static Version GetInstalledNodeVersion()
+        {
+            var versionString = InvokeNodeVersionCommand();
+            if (versionString == null)
+            {
+                return null;
+            }
+
+            var versionStringMatch = NodeVersionRegex.Match(versionString);
+            if (!versionStringMatch.Success)
+            {
+                Console.WriteLine($"ERROR: Got unparseable Node.js version string: {versionStringMatch}");
+                return null;
+            }
+
+            return new Version(versionStringMatch.Groups[1].Value);
+        }
+
+        private static string InvokeNodeVersionCommand()
+        {
+            try
+            {
+                var process = Process.Start(new ProcessStartInfo
+                {
+                    FileName = "node",
+                    Arguments = "-v",
+                    RedirectStandardOutput = true
+                });
+                process.WaitForExit();
+
+                if (process.ExitCode != 0)
+                {
+                    Console.WriteLine($"ERROR: The command 'node -v' exited with code {process.ExitCode}.");
+                    return null;
+                }
+                else
+                {
+                    return process.StandardOutput.ReadToEnd();
+                }
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine("ERROR: Node.js was not found. Ensure that Node.js is installed and that 'node' is present on the system PATH.");
+                Console.WriteLine("The underlying error was: " + ex.Message);
+                return null;
+            }
+        }
+    }
+}

src/Microsoft.Blazor.BuildTools/Microsoft.Blazor.BuildTools.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.CommandLineUtils" Version="1.1.1" />
+  </ItemGroup>
+
+</Project>

src/Microsoft.Blazor.BuildTools/Program.cs

@@ -0,0 +1,30 @@
+using Microsoft.Blazor.BuildTools.Cli;
+using Microsoft.Extensions.CommandLineUtils;
+using System;
+
+namespace Microsoft.Blazor.BuildTools
+{
+    static class Program
+    {
+        static int Main(string[] args)
+        {
+            var app = new CommandLineApplication
+            {
+                Name = "blazor-buildtools"
+            };
+            app.HelpOption("-?|-h|--help");
+
+            app.Command("checknodejs", CheckNodeJsInstalled.Command);
+
+            if (args.Length > 0)
+            {
+                return app.Execute(args);
+            }
+            else
+            {
+                app.ShowHelp();
+                return 0;
+            }
+        }
+    }
+}

src/Microsoft.Blazor.BuildTools/local.props

@@ -0,0 +1,7 @@
+<Project>
+  <PropertyGroup>
+    <!-- To avoid repeatedly running up-to-date checks, rely on the project already being built. -->
+    <!-- For this to work, consumers will need to have a project reference to this project. -->
+    <BlazorBuildTools>dotnet run --no-build --project $(MSBuildThisFileDirectory)</BlazorBuildTools>
+  </PropertyGroup>
+</Project>