title: TS2307: Cannot find module 'class-validator'
body: <p>I'm attempting to use the <a href="https://github.com/pleerock/class-validator" rel="nofollow noreferrer">class-validator</a> module in a typescript project.  However when I compile typescript issues the following warning:</p>
  
  <pre><code>src/main/ts/domain/Order.ts(1,48): error TS2307: Cannot find module 'class-validator'.
  </code></pre>
  
  <p>The line it is complaining about looks like this:</p>
  
  <pre><code>  import { IsInt, IsNotEmpty, IsDate, Min } from "class-validator";
  </code></pre>
  
  <p>I have gulp setup like this:</p>
  
  <pre><code>    var gulp = require('gulp');
      var ts = require('gulp-typescript');
      var tsProject = ts.createProject("tsconfig.json");
  
      gulp.task('default', function() {
        return tsProject.src()
          .pipe(tsProject())
          .js.pipe(gulp.dest("target/main/js"));
      });
  </code></pre>
  
  <p>And my tsconfig.json looks like this:</p>
  
  <pre><code>    {
          "files": [
              "src/main/ts/**/*.ts"
          ],
          "compilerOptions": {
              "experimentalDecorators": true,
              "noImplicitAny": true,
              "target": "es6"
          }
      }
  </code></pre>
  
  <p>Thoughts?</p>