refactor: better context creation API

packages/behavior/context/index.js

@@ -11,16 +11,19 @@ const debug = D('@avocado:behavior:context');
 
 export class Context {
 
-  constructor() {
+  constructor(defaults = {}) {
     this.map = new Map();
-    this.addDefaults();
+    this.addGlobalDefaults();
+    for (const key in defaults) {
+      this.add(key, defaults[key]);
+    }
   }
 
   add(key, value) {
     this.map.set(key, value);
   }
 
-  addDefaults() {
+  addGlobalDefaults() {
     this.add('context', this);
     this.add('Flow', Flow);
     this.add('Math', MathExt);
@@ -30,7 +33,7 @@ export class Context {
 
   clear() {
     this.map.clear();
-    this.addDefaults();
+    this.addGlobalDefaults();
   }
 
   destroy() {
@@ -81,7 +84,9 @@ export class Context {
       // Try to set the value.
       switch (step.type) {
         case 'key':
-          return node[step.key] = value.get(this);
+          if ('object' === typeof node) {
+            return node[step.key] = value.get(this);
+          }
         case 'invoke':
           const rendered = this.constructor.renderStepsUntilNow(steps, step);
           debug(`invalid assignment to function "${rendered}"`);

packages/behavior/traits/behaved.trait.js

@@ -32,8 +32,9 @@ export class Behaved extends decorate(Trait) {
 
   constructor(entity, params, state) {
     super(entity, params, state);
-    this._context = new Context();
-    this._context.add('entity', this.entity);
+    this._context = new Context({
+      entity: this.entity,
+    });
     this._currentRoutine = undefined;
     const routinesJSON = this.params.routines;
     this._routines = (new Routines()).fromJSON(routinesJSON);

packages/entity/traits/alive.trait.js

@@ -63,8 +63,9 @@ export class Alive extends decorate(Trait) {
 
   constructor(entity, params, state) {
     super(entity, params, state);
-    this._context = new Context();
-    this._context.add('entity', this.entity);
+    this._context = new Context({
+      entity: this.entity,
+    });
     const actionsJSON = this.params.deathActions;
     this._deathActions = behaviorItemFromJSON(actionsJSON);
     this._deathSound = this.params.deathSound;

packages/physics/traits/collider.trait.js

@@ -64,9 +64,10 @@ export class Collider extends decorate(Trait) {
 
   pushActionBundle(paramActions, other) {
     const actions = behaviorItemFromJSON(paramActions);
-    const context = new Context();
-    context.add('entity', this.entity);
-    context.add('other', other);
+    const context = new Context({
+      entity: this.entity,
+      other,
+    });
     const bundle = {
       actions,
       context,