review eslint core rules: enforce the use of variables within the scope they are defined

Author: zloirock

packages/core-js/internals/array-slice-simple.js

@@ -11,7 +11,8 @@ module.exports = function (O, start, end) {
   var k = toAbsoluteIndex(start, length);
   var fin = toAbsoluteIndex(end === undefined ? length : end, length);
   var result = $Array(max(fin - k, 0));
-  for (var n = 0; k < fin; k++, n++) createProperty(result, n, O[k]);
+  var n = 0;
+  for (; k < fin; k++, n++) createProperty(result, n, O[k]);
   result.length = n;
   return result;
 };

packages/core-js/internals/function-bind.js

@@ -13,7 +13,9 @@ var factories = {};
 
 var construct = function (C, argsLength, args) {
   if (!hasOwn(factories, argsLength)) {
-    for (var list = [], i = 0; i < argsLength; i++) list[i] = 'a[' + i + ']';
+    var list = [];
+    var i = 0;
+    for (; i < argsLength; i++) list[i] = 'a[' + i + ']';
     factories[argsLength] = $Function('C,a', 'return new C(' + join(list, ',') + ')');
   } return factories[argsLength](C, args);
 };

packages/core-js/modules/es.string.replace.js

@@ -88,13 +88,16 @@ fixRegExpWellKnownSymbolLogic('replace', function (_, nativeReplace, maybeCallNa
       if (!functionalReplace) replaceValue = toString(replaceValue);
 
       var global = rx.global;
+      var fullUnicode;
       if (global) {
-        var fullUnicode = rx.unicode;
+        fullUnicode = rx.unicode;
         rx.lastIndex = 0;
       }
+
       var results = [];
+      var result;
       while (true) {
-        var result = regExpExec(rx, S);
+        result = regExpExec(rx, S);
         if (result === null) break;
 
         push(results, result);
@@ -112,6 +115,7 @@ fixRegExpWellKnownSymbolLogic('replace', function (_, nativeReplace, maybeCallNa
         var matched = toString(result[0]);
         var position = max(min(toIntegerOrInfinity(result.index), S.length), 0);
         var captures = [];
+        var replacement;
         // NOTE: This is equivalent to
         //   captures = result.slice(1).map(maybeToString)
         // but for some reason `nativeSlice.call(result, 1, result.length)` (called in
@@ -122,7 +126,7 @@ fixRegExpWellKnownSymbolLogic('replace', function (_, nativeReplace, maybeCallNa
         if (functionalReplace) {
           var replacerArgs = concat([matched], captures, position, S);
           if (namedCaptures !== undefined) push(replacerArgs, namedCaptures);
-          var replacement = toString(apply(replaceValue, undefined, replacerArgs));
+          replacement = toString(apply(replaceValue, undefined, replacerArgs));
         } else {
           replacement = getSubstitution(matched, S, position, captures, namedCaptures, replaceValue);
         }
@@ -131,6 +135,7 @@ fixRegExpWellKnownSymbolLogic('replace', function (_, nativeReplace, maybeCallNa
           nextSourcePosition = position + matched.length;
         }
       }
+
       return accumulatedResult + stringSlice(S, nextSourcePosition);
     }
   ];

packages/core-js/modules/esnext.string.dedent.js

@@ -65,7 +65,7 @@ var dedentStringsArray = function (template) {
   var blocks = $Array(length);
   var dedented = $Array(length);
   var i = 0;
-  var lines, common;
+  var lines, common, quasi, k;
 
   if (!length) throw $TypeError(INVALID_TAG);
 
@@ -107,7 +107,9 @@ var dedentStringsArray = function (template) {
 
   for (i = 0; i < length; i++) {
     lines = blocks[i];
-    for (var quasi = lines[0], k = 1; k < lines.length; k += 2) {
+    quasi = lines[0];
+    k = 1;
+    for (; k < lines.length; k += 2) {
       quasi += lines[k] + stringSlice(lines[k + 1], count);
     }
     dedented[i] = quasi;
@@ -126,7 +128,10 @@ var commonLeadingIndentation = function (a, b) {
 };
 
 var cookStrings = function (raw) {
-  for (var i = 0, length = raw.length, result = $Array(length); i < length; i++) {
+  var i = 0;
+  var length = raw.length;
+  var result = $Array(length);
+  for (; i < length; i++) {
     result[i] = parse(raw[i]);
   } return result;
 };

tests/eslint/eslint.config.js

@@ -112,6 +112,8 @@ const base = {
   'valid-typeof': ERROR,
 
   // suggestions:
+  // enforce the use of variables within the scope they are defined
+  'block-scoped-var': ERROR,
   // require camel case names
   camelcase: [ERROR, { properties: NEVER }],
   // enforce default clauses in switch statements to be last