feat!: Populate additional preload modules with configFiles

README.md

@@ -594,6 +594,10 @@ All `extends` properties will be traversed and become the basis for the resultin
 
 Users can override the `configPath` via their config files by specifying a field with the same name as the primary `configName`. For example, the `hackerfile` property in a `configFile` will resolve the `configPath` and `configBase` against the path.
 
+### `preload`
+
+If specified as a string or array of strings, they will be added to the list of preloads in the environment.
+
 ## Examples
 
 Check out how [gulp][gulp-cli-index] uses Liftoff.

index.js

@@ -20,6 +20,10 @@ var buildConfigName = require('./lib/build_config_name');
 var registerLoader = require('./lib/register_loader');
 var getNodeFlags = require('./lib/get_node_flags');
 
+function isString(val) {
+  return typeof val === 'string';
+}
+
 function Liftoff(opts) {
   EE.call(this);
   extend(this, parseOptions(opts));
@@ -119,7 +123,7 @@ Liftoff.prototype.buildEnvironment = function (opts) {
     // resolve something like `{ gulpfile: "./abc.xyz" }` to the absolute path
     // based on the path of the configFile
     if (Object.prototype.hasOwnProperty.call(configFile, configName)) {
-      if (typeof configFile[configName] === 'string') {
+      if (isString(configFile[configName])) {
         configFile[configName] = path.resolve(path.dirname(configFilePath), configFile[configName]);
       }
     }
@@ -160,12 +164,26 @@ Liftoff.prototype.buildEnvironment = function (opts) {
   var configPathOverride = arrayFind(Object.keys(config), function (key) {
     var cfg = config[key];
     if (Object.prototype.hasOwnProperty.call(cfg, configName)) {
-      if (typeof cfg[configName] === "string") {
+      if (isString(cfg[configName])) {
         return cfg[configName];
       }
     }
   });
 
+  var additionPreloads = arrayFind(Object.keys(config), function (key) {
+    var cfg = config[key];
+    if (Object.prototype.hasOwnProperty.call(cfg, 'preload')) {
+      if (Array.isArray(cfg.preload)) {
+        if (cfg.preload.every(isString)) {
+          return cfg.preload;
+        }
+      }
+      if (isString(cfg.preload)) {
+        return cfg.preload;
+      }
+    }
+  });
+
   // if cwd was provided explicitly, only use it for searching config
   if (opts.cwd) {
     searchPaths = [cwd];
@@ -233,7 +251,7 @@ Liftoff.prototype.buildEnvironment = function (opts) {
 
   return {
     cwd: cwd,
-    preload: preload,
+    preload: preload.concat(additionPreloads || []),
     completion: opts.completion,
     configNameSearch: configNameSearch,
     configPath: configPath,

test/index.js

@@ -616,6 +616,100 @@ describe('Liftoff', function () {
       });
     });
 
+    it('adds array of preloads specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-array': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({}, function (env) {
+        expect(env.preload).toEqual(['abc', 'xyz']);
+        done();
+      });
+    });
+
+    it('combines array of preloads specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-array': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({
+        preload: ['123']
+      }, function (env) {
+        expect(env.preload).toEqual(['123', 'abc', 'xyz']);
+        done();
+      });
+    });
+
+    it('adds string preload specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-string': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({}, function (env) {
+        expect(env.preload).toEqual(['abc']);
+        done();
+      });
+    });
+
+    it('combines string preload specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-string': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({
+        preload: ['xyz']
+      }, function (env) {
+        expect(env.preload).toEqual(['xyz', 'abc']);
+        done();
+      });
+    });
+
+    it('ignores non-string/non-array preload specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-invalid': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({}, function (env) {
+        expect(env.preload).toEqual([]);
+        done();
+      });
+    });
+
+    it('ignores array with any non-strings preload specified in config', function (done) {
+      var app = new Liftoff({
+        name: 'myapp',
+        configFiles: {
+          'preload-invalid-array': [
+            { path: 'test/fixtures/configfiles', extensions: ['.js'] }
+          ],
+        },
+      });
+      app.prepare({}, function (env) {
+        expect(env.preload).toEqual([]);
+        done();
+      });
+    });
+
     it('should use dirname of configPath if no cwd is specified', function (done) {
       var app = new Liftoff({
         name: 'myapp',