diff --git a/core/block.ts b/core/block.ts
index 9037345ae57..f226105ebfc 100644
--- a/core/block.ts
+++ b/core/block.ts
@@ -1309,7 +1309,7 @@ export class Block implements IASTNodeLocation, IDeletable {
    * @return Text of block.
    */
   toString(opt_maxLength?: number, opt_emptyToken?: string): string {
-    let text = [];
+    const text = [];
     const emptyFieldPlaceholder = opt_emptyToken || '?';
 
     // Temporarily set flag to navigate to all fields.
@@ -1397,26 +1397,20 @@ export class Block implements IASTNodeLocation, IDeletable {
     }
 
     // Join the text array, removing spaces around added parentheses.
-    // AnyDuringMigration because:  Type 'string' is not assignable to type
-    // 'any[]'.
-    text = text.reduce(function(acc, value) {
+    let combinedText: string = text.reduce(function(acc, value) {
       return acc + (acc.substr(-1) === '(' || value === ')' ? '' : ' ') + value;
-    }, '') as AnyDuringMigration;
-    // AnyDuringMigration because:  Property 'trim' does not exist on type
-    // 'any[]'.
-    text = (text as AnyDuringMigration).trim() || '???';
+    }, '');
+
+    combinedText = combinedText.trim() || '???';
     if (opt_maxLength) {
       // TODO: Improve truncation so that text from this block is given
       // priority. E.g. "1+2+3+4+5+6+7+8+9=0" should be "...6+7+8+9=0", not
       // "1+2+3+4+5...". E.g. "1+2+3+4+5=6+7+8+9+0" should be "...4+5=6+7...".
-      if (text.length > opt_maxLength) {
-        // AnyDuringMigration because:  Type 'string' is not assignable to type
-        // 'any[]'.
-        text = (text.substring(0, opt_maxLength - 3) + '...') as
-            AnyDuringMigration;
+      if (combinedText.length > opt_maxLength) {
+        combinedText = combinedText.substring(0, opt_maxLength - 3) + '...';
       }
     }
-    return text;
+    return combinedText;
   }
 
   /**
diff --git a/core/field_registry.ts b/core/field_registry.ts
index 2cf98a32b37..31f37783a42 100644
--- a/core/field_registry.ts
+++ b/core/field_registry.ts
@@ -68,7 +68,7 @@ export function fromJson(options: AnyDuringMigration): Field|null {
  */
 function fromJsonInternal(options: AnyDuringMigration): Field|null {
   const fieldObject =
-      registry.getObject(registry.Type.FIELD, options['type']) as
+      registry.getObject(registry.Type.FIELD, options['type']) as unknown as
           IRegistrableField |
       null;
   if (!fieldObject) {
diff --git a/core/generator.ts b/core/generator.ts
index 44d53e1e0bf..2e098331714 100644
--- a/core/generator.ts
+++ b/core/generator.ts
@@ -120,7 +120,7 @@ export class Generator {
           'No workspace specified in workspaceToCode call.  Guessing.');
       workspace = common.getMainWorkspace();
     }
-    let code = [];
+    const lines = [];
     this.init(workspace);
     const blocks = workspace.getTopBlocks(true);
     for (let i = 0, block; block = blocks[i]; i++) {
@@ -144,21 +144,13 @@ export class Generator {
             line = line + this.injectId(this.STATEMENT_SUFFIX, block);
           }
         }
-        code.push(line);
+        lines.push(line);
       }
     }
-    // AnyDuringMigration because:  Type 'string' is not assignable to type
-    // 'any[]'.
-    // Blank line between each section.
-    code = code.join('\n') as AnyDuringMigration;
-    // AnyDuringMigration because:  Argument of type 'any[]' is not assignable
-    // to parameter of type 'string'. AnyDuringMigration because:  Type 'string'
-    // is not assignable to type 'any[]'.
-    code = this.finish(code as AnyDuringMigration) as AnyDuringMigration;
-    // Final scrubbing of whitespace.
-    // AnyDuringMigration because:  Property 'replace' does not exist on type
-    // 'any[]'.
-    code = (code as AnyDuringMigration).replace(/^\s+\n/, '');
+
+    let code = lines.join('\n');
+    code = this.finish(code);
+    code = code.replace(/^\s+\n/, '');
     code = code.replace(/\n\s+$/, '\n');
     code = code.replace(/[ \t]+\n/g, '\n');
     return code;
diff --git a/core/utils/toolbox.ts b/core/utils/toolbox.ts
index c3834fd8b0a..7fa14843f39 100644
--- a/core/utils/toolbox.ts
+++ b/core/utils/toolbox.ts
@@ -403,20 +403,18 @@ function addAttributes(node: Node, obj: AnyDuringMigration) {
  */
 export function parseToolboxTree(toolboxDef: Element|null|string): Element|
     null {
+  let parsedToolboxDef: Element|null = null;
   if (toolboxDef) {
-    if (typeof toolboxDef !== 'string' && !(toolboxDef instanceof Element)) {
-      toolboxDef = null;
-    }
     if (typeof toolboxDef === 'string') {
-      toolboxDef = Xml.textToDom(toolboxDef);
-      if (toolboxDef.nodeName.toLowerCase() !== 'xml') {
+      parsedToolboxDef = Xml.textToDom(toolboxDef);
+      if (parsedToolboxDef.nodeName.toLowerCase() !== 'xml') {
         throw TypeError('Toolbox should be an <xml> document.');
       }
+    } else if (toolboxDef instanceof Element) {
+      parsedToolboxDef = toolboxDef;
     }
-  } else {
-    toolboxDef = null;
   }
-  return toolboxDef;
+  return parsedToolboxDef;
 }
 
 export const TEST_ONLY = {