feat: string/ensure

README.md

@@ -35,6 +35,18 @@ stringCoerce(12); // "12"
 stringCoerce(undefined); // null
 ```
 
+##### `string/ensure`
+
+If given argument is a string coercible value, returns string representation.
+Otherwise `TypeError` is thrown.
+
+```javascript
+const ensureString = require("type/string/ensure");
+
+ensureString(12); // "12"
+ensureString(null); // Thrown TypeError: null is not a string
+```
+
 #### Value
 
 _Value_ is assumed to be any JavaScript value that's neither `null` nor `undefined` (_the only primitives which are not accompanied with object representation. Hence any property access on them (as e.g. `null.foo`) results with an exception_)

string/ensure.js

@@ -0,0 +1,10 @@
+"use strict";
+
+var resolveException = require("../lib/resolve-exception")
+  , coerce           = require("./coerce");
+
+module.exports = function (value/*, options*/) {
+	var coerced = coerce(value);
+	if (coerced !== null) return coerced;
+	return resolveException(value, "%v is not a string", arguments[1]);
+};

test/string/ensure.js

@@ -0,0 +1,17 @@
+"use strict";
+
+var assert       = require("chai").assert
+  , ensureString = require("../../string/ensure");
+
+describe("string/ensure", function () {
+	it("Should return coerced value", function () { assert.equal(ensureString(12), "12"); });
+	it("Should crash on no value", function () {
+		try {
+			ensureString(null);
+			throw new Error("Unexpected");
+		} catch (error) {
+			assert.equal(error.name, "TypeError");
+			assert.equal(error.message, "null is not a string");
+		}
+	});
+});