try allowing binary expressions (being careful about recent changes to upstream eslint)

lib/rules/no-unsafe-innerhtml.js

@@ -56,6 +56,9 @@ module.exports = function (context) {
           if (VALID_UNWRAPPERS.indexOf(funcName) !== -1) {
             allowed = true;
           }
+        } else if (expression.type == "BinaryExpression") {
+          allowed = ((allowedExpression(expression.left, expression))
+                      && (allowedExpression(expression.right, expression)));
         } else {
             // everything that doesn't match is unsafe:
             allowed = false;

package.json

@@ -10,7 +10,7 @@
     },
     "devDependencies": {
         "eslint": ">=0.24.0",
-        "eslint-tester": ">=0.8.2",
+        "eslint-tester": "0.8.1",
         "mocha": "^2.2.4"
     },
     "dependencies": {

tests/rules/no-unsafe-innerhtml.js

@@ -93,6 +93,15 @@ eslintTester.addRuleTest("lib/rules/no-unsafe-innerhtml", {
         {
             code: "g.innerHTML = potentiallyUnsafe; // a=legacy, bug 1155131",
             ecmaFeatures: { templateStrings: true }
+        },
+        // (binary) expressions
+        {
+            code: "x.innerHTML = `foo`+`bar`;",
+            ecmaFeatures: { templateStrings: true }
+        },
+        {
+            code: "y.innerHTML = '<span>' + 5 + '</span>';",
+            ecmaFeatures: { templateStrings: true }
         }
     ],
 
@@ -157,6 +166,25 @@ eslintTester.addRuleTest("lib/rules/no-unsafe-innerhtml", {
                     type: "CallExpression"
                 }
             ]
+        },
+        // (binary) expressions
+        {
+            code: "node.innerHTML = '<span>'+ htmlInput;",
+            errors: [
+                {
+                    message: "Unsafe assignment to innerHTML",
+                    type: "AssignmentExpression"
+                }
+            ]
+        },
+        {
+            code: "node.innerHTML = '<span>'+ htmlInput + '</span>';",
+            errors: [
+                {
+                    message: "Unsafe assignment to innerHTML",
+                    type: "AssignmentExpression"
+                }
+            ]
         }
     ]
 });