feat: number/coerce

README.md

@@ -67,6 +67,28 @@ ensureString(12); // "12"
 ensureString(null); // Thrown TypeError: null is not a string
 ```
 
+#### Number
+
+_number_ primitives
+
+##### `number/coerce`
+
+Restricted number coercion. Returns number presentation for every value that follows below constraints
+
+-   is implicitly coercible to number
+-   is neither `null` nor `undefined`
+-   is not and doesn't coerce to `NaN`
+
+For all other values `null` is returned
+
+```javascript
+const numberCoerce = require("type/number/coerce");
+
+numberCoerce("12"); // 12
+numberCoerce({}); // null
+numberCoerce(null); // null
+```
+
 #### Object
 
 _Object_ is assumed to be any non-primitive JavaScript value

number/coerce.js

@@ -0,0 +1,14 @@
+"use strict";
+
+var isValue = require("../value/is");
+
+module.exports = function (value) {
+	if (!isValue(value)) return null;
+	try {
+		value = +value; // Ensure implicit coercion
+	} catch (error) {
+		return null;
+	}
+	if (isNaN(value)) return null;
+	return value;
+};

package.json

@@ -49,7 +49,10 @@
 				}
 			},
 			{
-				"files": "string/coerce.js",
+				"files": [
+					"string/coerce.js",
+					"number/coerce.js"
+				],
 				"rules": {
 					"no-implicit-coercion": "off"
 				}

test/number/coerce.js

@@ -0,0 +1,33 @@
+"use strict";
+
+var assert       = require("chai").assert
+  , numberCoerce = require("../../number/coerce");
+
+describe("number/coerce", function () {
+	it("Should return input number", function () { assert.equal(numberCoerce(123.123), 123.123); });
+	it("Should coerce string", function () { assert.equal(numberCoerce("12"), 12); });
+	it("Should coerce booleans", function () { assert.equal(numberCoerce(true), 1); });
+	it("Should coerce number objects", function () {
+		assert.equal(numberCoerce(new Number(343)), 343);
+	});
+	it("Should coerce objects", function () {
+		assert.equal(numberCoerce({ valueOf: function () { return 23; } }), 23);
+	});
+
+	it("Should reject NaN", function () { assert.equal(numberCoerce(NaN), null); });
+
+	if (typeof Object.create === "function") {
+		it("Should not coerce objects with no number representation", function () {
+			assert.equal(numberCoerce(Object.create(null)), null);
+		});
+	}
+
+	it("Should not coerce null", function () { assert.equal(numberCoerce(null), null); });
+	it("Should not coerce undefined", function () { assert.equal(numberCoerce(undefined), null); });
+
+	if (typeof Symbol === "function") {
+		it("Should not coerce symbols", function () {
+			assert.equal(numberCoerce(Symbol("foo")), null);
+		});
+	}
+});