Style / add an ol/style/expressions module

This module will contain the utilities and operator declarations
for literal style expressions, boh for type checking and parsing

test/spec/ol/style/expressions.test.js

@@ -0,0 +1,41 @@
+import {getValueType, ValueTypes} from '../../../../src/ol/style/expressions.js';
+
+
+describe('ol.style.expressions', function() {
+
+  describe('getValueType', function() {
+
+    it('correctly analyzes a literal value', function() {
+      expect(getValueType(1234)).to.eql(ValueTypes.NUMBER);
+      expect(getValueType([1, 2, 3, 4])).to.eql(ValueTypes.COLOR | ValueTypes.NUMBER_ARRAY);
+      expect(getValueType([1, 2, 3])).to.eql(ValueTypes.COLOR | ValueTypes.NUMBER_ARRAY);
+      expect(getValueType([1, 2])).to.eql(ValueTypes.NUMBER_ARRAY);
+      expect(getValueType([1, 2, 3, 4, 5])).to.eql(ValueTypes.NUMBER_ARRAY);
+      expect(getValueType('yellow')).to.eql(ValueTypes.COLOR | ValueTypes.STRING);
+      expect(getValueType('#113366')).to.eql(ValueTypes.COLOR | ValueTypes.STRING);
+      expect(getValueType('rgba(252,171,48,0.62)')).to.eql(ValueTypes.COLOR | ValueTypes.STRING);
+      expect(getValueType('abcd')).to.eql(ValueTypes.STRING);
+      expect(getValueType(true)).to.eql(ValueTypes.BOOLEAN);
+    });
+
+    it('throws on an unsupported type (object)', function(done) {
+      try {
+        getValueType(new Object());
+      } catch (e) {
+        done();
+      }
+      done(true);
+    });
+
+    it('throws on an unsupported type (mixed array)', function(done) {
+      try {
+        getValueType([1, true, 'aa']);
+      } catch (e) {
+        done();
+      }
+      done(true);
+    });
+
+  });
+
+});