feat: value/is

README.md

@@ -1,3 +1,24 @@
 # type
 
 ## Runtime validation and processing of JavaScript types
+
+### Installation
+
+```sh
+npm install type
+```
+
+#### Value
+
+_Value_ is assumed to be any JavaScript value that's neither `null` nor `undefined` (the only primitives not accompanied with object representation. Hence any property access on them (as e.g. `null.foo`) results with an exception)
+
+`undefined` usually means that given variable or property was never defined, while `null` reflects declared intention of having given property or variable empty.
+
+##### `value/is`
+
+```javascript
+const isValue = require("type/value/is");
+
+isValue({}); // true
+isValue(null); // false
+```

test/value/is.js

@@ -0,0 +1,29 @@
+"use strict";
+
+var assert  = require("chai").assert
+  , isValue = require("../../value/is");
+
+describe("value/is", function () {
+	it("Should return true on object", function () { assert.equal(isValue({}), true); });
+	it("Should return true on function", function () {
+		assert.equal(isValue(function () { return true; }), true);
+	});
+	it("Should return true on array", function () { assert.equal(isValue([]), true); });
+	if (typeof Object.create === "function") {
+		it("Should return true on object with no prototype", function () {
+			assert.equal(isValue(Object.create(null)), true);
+		});
+	}
+	it("Should return true on string", function () { assert.equal(isValue("foo"), true); });
+	it("Should return true on empty string", function () { assert.equal(isValue(""), true); });
+	it("Should return true on number", function () { assert.equal(isValue(123), true); });
+	it("Should return true on NaN", function () { assert.equal(isValue(NaN), true); });
+	it("Should return true on boolean", function () { assert.equal(isValue(false), true); });
+	if (typeof Symbol === "function") {
+		// eslint-disable-next-line no-undef
+		it("Should return true on symbol", function () { assert.equal(isValue(Symbol()), true); });
+	}
+
+	it("Should return false on null", function () { assert.equal(isValue(null), false); });
+	it("Should return false on undefined", function () { assert.equal(isValue(void 0), false); });
+});

value/is.js

@@ -0,0 +1,6 @@
+"use strict";
+
+// ES3 safe
+var _undefined = void 0;
+
+module.exports = function (value) { return value !== _undefined && value !== null; };