'confusing minuses' article

Author: James Allardice

articles.md

@@ -208,7 +208,7 @@ the filename of the new article next to it.
  - `already-defined.md` - ~~'{a}' is already defined~~
  - `valid-trailing-decimal.md` - ~~A dot following a number can be confused with
    a decimal point~~
- - Confusing minuses
+ - `confusing-minuses.md` - ~~Confusing minuses~~
  - `confusing-pluses.md` - ~~Confusing pluses~~
  - `leading-decimal.md` - ~~A leading decimal point can be confused with a dot~~
  - `array-literal-notation.md` - ~~he array literal notation [] is preferable~~

articles/confusing-minuses.md

@@ -0,0 +1,100 @@
+<!---
+{
+    "titles": [
+        "Confusing minuses",
+        "W006"
+    ],
+    "slugs": [
+        "confusing-minuses",
+        "w006"
+    ],
+    "linters": [
+        "jslint",
+        "jshint"
+    ],
+    "author": "jallardice"
+}
+-->
+
+### History
+
+This warning has existed in a few forms in both JSLint and JSHint. It was
+introduced in the original version of JSLint and has remained in both tools ever
+since.
+
+ - In JSHint prior to version 1.0.0 the warning given was *"Confusing minusses"*
+
+ - In JSHint 1.0.0 and above the spelling has been corrected and the message
+   used is now *"Confusing minuses"*
+
+ - JSLint has always used the more generic *"Confusing use of '{a}"* warning in
+   the same situation
+
+### When do I get this error?
+
+The "Confusing minuses" error is thrown when JSHint encounters **an addition
+operator in which the right-hand-side expression is preceded by the unary `-`
+operator**. In the following example we attempt to compute the addition of a
+numeric literal and the numeric value of a variable:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+var a = "10",
+    b = 5 - -a;
+```
+
+### Why do I get this error?
+
+This error is raised to highlight a **potentially confusing piece of code**.
+Your code will most likely run as expected but it could cause issues with
+maintenance and be confusing to other developers.
+
+The `-` operator is overloaded in JavaScript. Most commonly it can be seen as
+the subtraction operator but it also functions in a unary form as a numeric
+casting and negating operator. In this unary form the result of the expression
+will be the value of the operand coerced to the Number type and then negated. In
+the example above, because the value of `a` is a string that can be converted to
+a number, the `+a` expression results in the value `-10` and the value of `b`
+ends up as `-5`.
+
+This behaviour is described in the specification ([ES5
+&sect;11.4.7][es5-11.4.7]):
+
+> The production *UnaryExpression* : `-` *UnaryExpression* is evaluated as
+> follows:
+> 1. Let *expr* be the result of evaluating UnaryExpression.
+> 2. Let *oldValue* be ToNumber(GetValue(*expr*)).
+> 3. If *oldValue* is NaN, return NaN.
+> 4. Return the result of negating *oldValue*; that is, compute a Number with
+> the same magnitude but opposite sign.
+
+However, when the subtraction operator is used adjacent to the unary `-`
+operator an unforunate resemblance to the decrement operator arises. The
+decrement operator, `--`, is used to subtract 1 from its operand. It can be used
+as a postfix or prefix operator which means it can appear after or before its
+operand. This makes the above example slightly confusing on first glance.
+
+To resolve this issue the easiest fix is to wrap the unary expression in
+parentheses to disambiguate the `-` characters:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+var a = "10",
+    b = 5 - (-a);
+```
+
+In JSHint 1.0.0 and above you have the ability to ignore any warning with a
+[special option syntax][jshintopts]. The identifier of this warning is **W006**.
+This means you can tell JSHint to not issue this warning with the `/*jshint
+-W006 */` directive.
+
+[es5-11.4.7]: http://es5.github.io/#x11.4.7
+[jshintopts]: http://jshint.com/docs/#options