Fixed #1465: toHTML() not correct for unary operators

HISTORY.md

@@ -4,6 +4,8 @@
 # not yet released, version 5.9.0
 
 - Implemented functions `row` and `column` (see #1413). Thanks @SzechuanSage.
+- Fixed #1465: `node.toHTML()` not correct for unary operators like
+  `factorial`.
 
 
 # 2019-03-20, version 5.8.0

src/expression/node/OperatorNode.js

@@ -463,12 +463,9 @@ function factory (type, config, load, typed) {
 
       if (assoc === 'right') { // prefix operator
         return '<span class="math-operator math-unary-operator math-lefthand-unary-operator">' + escape(this.op) + '</span>' + operand
-      } else if (assoc === 'left') { // postfix
-        return '<span class="math-operator math-unary-operator math-righthand-unary-operator">' + escape(this.op) + '</span>' + operand
+      } else { // postfix when assoc === 'left' or undefined
+        return operand + '<span class="math-operator math-unary-operator math-righthand-unary-operator">' + escape(this.op) + '</span>'
       }
-
-      // fall back to postfix
-      return '<span class="math-operator math-unary-operator math-righthand-unary-operator">' + escape(this.op) + '</span>' + operand
     } else if (args.length === 2) { // binary operatoes
       let lhs = args[0].toHTML(options) // left hand side
       let rhs = args[1].toHTML(options) // right hand side

test/expression/node/OperatorNode.test.js

@@ -766,6 +766,29 @@ describe('OperatorNode', function () {
     assert.strictEqual(h.toTex({ implicit: 'show' }), '2\\cdot\\left(3+4\\right)')
   })
 
+  it('should HTML operators', function () {
+    assert.strictEqual(math.parse('2 + 3').toHTML(),
+      '<span class="math-number">2</span>' +
+      '<span class="math-operator math-binary-operator math-explicit-binary-operator">+</span>' +
+      '<span class="math-number">3</span>'
+    )
+
+    assert.strictEqual(math.parse('not 5').toHTML(),
+      '<span class="math-operator math-unary-operator math-lefthand-unary-operator">not</span>' +
+      '<span class="math-number">5</span>'
+    )
+
+    assert.strictEqual(math.parse('5!').toHTML(),
+      '<span class="math-number">5</span>' +
+      '<span class="math-operator math-unary-operator math-righthand-unary-operator">!</span>'
+    )
+
+    assert.strictEqual(math.parse('5\'').toHTML(),
+      '<span class="math-number">5</span>' +
+      '<span class="math-operator math-unary-operator math-righthand-unary-operator">&#39;</span>'
+    )
+  })
+
   it('should stringify implicit multiplications between ConstantNodes with parentheses', function () {
     const a = math.parse('(4)(4)(4)(4)')
     const b = math.parse('4b*4(4)')