enhance comparisons (#5358)

lib/compress.js

@@ -3739,8 +3739,9 @@ Compressor.prototype.compress = function(node) {
         function join_assigns(defn, body, keep) {
             var exprs = extract_exprs(body);
             if (!exprs) return;
+            keep = keep || 0;
             var trimmed = false;
-            for (var i = exprs.length - (keep || 0); --i >= 0;) {
+            for (var i = exprs.length - keep; --i >= 0;) {
                 var expr = exprs[i];
                 if (!can_trim(expr)) continue;
                 var tail;
@@ -3762,7 +3763,6 @@ Compressor.prototype.compress = function(node) {
                 exprs = exprs.slice(0, i).concat(expr, tail);
             }
             if (defn instanceof AST_Definitions) {
-                keep = keep || 0;
                 for (var i = defn.definitions.length; --i >= 0;) {
                     var def = defn.definitions[i];
                     if (!def.value) continue;
@@ -11079,30 +11079,20 @@ Compressor.prototype.compress = function(node) {
             // void 0 !== x && null !== x ---> null != x
             // void 0 === x || null === x ---> null == x
             var lhs = self.left;
-            if (lhs.operator == self.operator) {
-                lhs = lhs.right;
-            }
+            if (lhs.operator == self.operator) lhs = lhs.right;
+            var expr = lhs.right;
+            if (expr instanceof AST_Assign && expr.operator == "=") expr = expr.left;
             if (lhs instanceof AST_Binary
                 && lhs.operator == (self.operator == "&&" ? "!==" : "===")
                 && self.right instanceof AST_Binary
                 && lhs.operator == self.right.operator
                 && (is_undefined(lhs.left, compressor) && self.right.left instanceof AST_Null
                     || lhs.left instanceof AST_Null && is_undefined(self.right.left, compressor))
-                && !lhs.right.has_side_effects(compressor)
-                && lhs.right.equivalent_to(self.right.right)) {
-                var combined = make_node(AST_Binary, self, {
-                    operator: lhs.operator.slice(0, -1),
-                    left: make_node(AST_Null, self),
-                    right: lhs.right
-                });
-                if (lhs !== self.left) {
-                    combined = make_node(AST_Binary, self, {
-                        operator: self.operator,
-                        left: self.left.left,
-                        right: combined
-                    });
-                }
-                return combined;
+                && !expr.has_side_effects(compressor)
+                && expr.equivalent_to(self.right.right)) {
+                lhs.operator = lhs.operator.slice(0, -1);
+                lhs.left = make_node(AST_Null, self);
+                return self.left;
             }
             break;
         }

test/benchmark.js

@@ -17,6 +17,7 @@ var urls = [
     "https://unpkg.com/mathjs@6.2.3/dist/math.js",
     "https://unpkg.com/react@15.3.2/dist/react.js",
     "https://cdnjs.cloudflare.com/ajax/libs/d3/6.7.0/d3.js",
+    "https://cdnjs.cloudflare.com/ajax/libs/antd/4.18.7/antd.js",
     "https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.js",
     "https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.js",
     "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.12.2/ember.prod.js",

test/compress/comparisons.js

@@ -493,3 +493,32 @@ issue_3413: {
     }
     expect_stdout: "PASS"
 }
+
+nullish_assign: {
+    options = {
+        comparisons: true,
+    }
+    input: {
+        var a;
+        void 0 !== (a = "PASS".split("")) && null !== a && console.log(a.join("-"));
+    }
+    expect: {
+        var a;
+        null != (a = "PASS".split("")) && console.log(a.join("-"));
+    }
+    expect_stdout: "P-A-S-S"
+}
+
+nullish_chain: {
+    options = {
+        comparisons: true,
+    }
+    input: {
+        var a;
+        A || B || void 0 === a || null === a || C;
+    }
+    expect: {
+        var a;
+        A || B || null == a || C;
+    }
+}