refactor(@angular-devkit/build-optimizer): use type guards in scrub file

Author: alan-agius4

packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts

@@ -47,15 +47,13 @@ function scrubFileTransformer(program: ts.Program | undefined, isAngularCoreFile
       ts.forEachChild(sf, checkNodeForDecorators);
 
       function checkNodeForDecorators(node: ts.Node): void {
-        if (node.kind !== ts.SyntaxKind.ExpressionStatement) {
-          // TS 2.4 nests decorators inside downleveled class IIFEs, so we
-          // must recurse into them to find the relevant expression statements.
+        if (!ts.isExpressionStatement(node)) {
           return ts.forEachChild(node, checkNodeForDecorators);
         }
+
         const exprStmt = node as ts.ExpressionStatement;
         // Do checks that don't need the typechecker first and bail early.
-        if (isIvyPrivateCallExpression(exprStmt)
-          || isCtorParamsAssignmentExpression(exprStmt)) {
+        if (isIvyPrivateCallExpression(exprStmt) || isCtorParamsAssignmentExpression(exprStmt)) {
           nodes.push(node);
         } else if (isDecoratorAssignmentExpression(exprStmt)) {
           nodes.push(...pickDecorationNodesToRemove(exprStmt, ngMetadata, checker));
@@ -360,7 +358,7 @@ function pickDecorationNodesToRemove(
   const expr = expect<ts.BinaryExpression>(exprStmt.expression, ts.SyntaxKind.BinaryExpression);
   const literal = expect<ts.ArrayLiteralExpression>(expr.right,
     ts.SyntaxKind.ArrayLiteralExpression);
-  if (!literal.elements.every((elem) => elem.kind === ts.SyntaxKind.ObjectLiteralExpression)) {
+  if (!literal.elements.every(elem => ts.isObjectLiteralExpression(elem))) {
     return [];
   }
   const elements = literal.elements as ts.NodeArray<ts.ObjectLiteralExpression>;
@@ -451,8 +449,8 @@ function pickPropDecorationNodesToRemove(
   const expr = expect<ts.BinaryExpression>(exprStmt.expression, ts.SyntaxKind.BinaryExpression);
   const literal = expect<ts.ObjectLiteralExpression>(expr.right,
     ts.SyntaxKind.ObjectLiteralExpression);
-  if (!literal.properties.every((elem) => elem.kind === ts.SyntaxKind.PropertyAssignment &&
-    (elem as ts.PropertyAssignment).initializer.kind === ts.SyntaxKind.ArrayLiteralExpression)) {
+  if (!literal.properties.every(elem => ts.isPropertyAssignment(elem)
+    && ts.isArrayLiteralExpression(elem.initializer))) {
     return [];
   }
   const assignments = literal.properties as ts.NodeArray<ts.PropertyAssignment>;
@@ -482,8 +480,7 @@ function pickPropDecorationNodesToRemove(
   // If every node to be removed is a property assignment (full property's decorators) and
   // all properties are accounted for, remove the whole assignment. Otherwise, remove the
   // nodes which were marked as safe.
-  if (toRemove.length === assignments.length &&
-    toRemove.every((node) => node.kind === ts.SyntaxKind.PropertyAssignment)) {
+  if (toRemove.length === assignments.length && toRemove.every((node) => ts.isPropertyAssignment(node))) {
     return [exprStmt];
   }