APIs for getting and setting variable values

src/engine/target.js

@@ -154,7 +154,7 @@ class Target extends EventEmitter {
         // If the stage has a global copy, return it.
         if (this.runtime && !this.isStage) {
             const stage = this.runtime.getTargetForStage();
-            if (stage.variables.hasOwnProperty(id)) {
+            if (stage && stage.variables.hasOwnProperty(id)) {
                 return stage.variables[id];
             }
         }

src/virtual-machine.js

@@ -1071,6 +1071,42 @@ class VirtualMachine extends EventEmitter {
             this.editingTarget.postSpriteInfo(data);
         }
     }
+
+    /**
+     * Set a target's variable's value. Return whether it succeeded.
+     * @param {!string} targetId ID of the target which owns the variable.
+     * @param {!string} variableId ID of the variable to set.
+     * @param {!*} value The new value of that variable.
+     * @returns {boolean} whether the target and variable were found and updated.
+     */
+    setVariableValue (targetId, variableId, value) {
+        const target = this.runtime.getTargetById(targetId);
+        if (target) {
+            const variable = target.lookupVariableById(variableId);
+            if (variable) {
+                variable.value = value;
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Get a target's variable's value. Return null if the target or variable does not exist.
+     * @param {!string} targetId ID of the target which owns the variable.
+     * @param {!string} variableId ID of the variable to set.
+     * @returns {?*} The value of the variable, or null if it could not be looked up.
+     */
+    getVariableValue (targetId, variableId) {
+        const target = this.runtime.getTargetById(targetId);
+        if (target) {
+            const variable = target.lookupVariableById(variableId);
+            if (variable) {
+                return variable.value;
+            }
+        }
+        return null;
+    }
 }
 
 module.exports = VirtualMachine;

test/unit/virtual-machine.js

@@ -1,6 +1,7 @@
 const test = require('tap').test;
 const VirtualMachine = require('../../src/virtual-machine.js');
 const Sprite = require('../../src/sprites/sprite.js');
+const Variable = require('../../src/engine/variable.js');
 
 test('addSprite throws on invalid string', t => {
     const vm = new VirtualMachine();
@@ -452,3 +453,46 @@ test('select original after dragging clone', t => {
     t.equal(newEditingTargetId, 'sprite1_original');
     t.end();
 });
+
+test('setVariableValue', t => {
+    const vm = new VirtualMachine();
+    const spr = new Sprite(null, vm.runtime);
+    const target = spr.createClone();
+    target.createVariable('a-variable', 'a-name', Variable.SCALAR_TYPE);
+
+    vm.runtime.targets = [target];
+
+    // Returns false if there is no variable to set
+    t.equal(vm.setVariableValue(target.id, 'not-a-variable', 100), false);
+
+    // Returns false if there is no target with that id
+    t.equal(vm.setVariableValue('not-a-target', 'a-variable', 100), false);
+
+    // Returns true and updates the value if variable is present
+    t.equal(vm.setVariableValue(target.id, 'a-variable', 100), true);
+    t.equal(target.lookupVariableById('a-variable').value, 100);
+
+    t.end();
+});
+
+test('getVariableValue', t => {
+    const vm = new VirtualMachine();
+    const spr = new Sprite(null, vm.runtime);
+    const target = spr.createClone();
+    target.createVariable('a-variable', 'a-name', Variable.SCALAR_TYPE);
+
+    vm.runtime.targets = [target];
+
+    // Returns null if there is no variable with that id
+    t.equal(vm.getVariableValue(target.id, 'not-a-variable'), null);
+
+    // Returns null if there is no variable with that id
+    t.equal(vm.getVariableValue('not-a-target', 'a-variable'), null);
+
+    // Returns true and updates the value if variable is present
+    t.equal(vm.getVariableValue(target.id, 'a-variable'), 0);
+    vm.setVariableValue(target.id, 'a-variable', 'string');
+    t.equal(vm.getVariableValue(target.id, 'a-variable'), 'string');
+
+    t.end();
+});