Use ES2021 Array.at

src/jsutils/formatList.ts

@@ -25,6 +25,6 @@ function formatList(conjunction: string, items: ReadonlyArray<string>): string {
   }
 
   const allButLast = items.slice(0, -1);
-  const lastItem = items[items.length - 1];
+  const lastItem = items.at(-1);
   return allButLast.join(', ') + ', ' + conjunction + ' ' + lastItem;
 }

src/language/__tests__/lexer-test.ts

@@ -1134,7 +1134,7 @@ describe('Lexer', () => {
     for (let tok: Token | null = startToken; tok; tok = tok.next) {
       if (tokens.length) {
         // Tokens are double-linked, prev should point to last seen token.
-        expect(tok.prev).to.equal(tokens[tokens.length - 1]);
+        expect(tok.prev).to.equal(tokens.at(-1));
       }
       tokens.push(tok);
     }

src/language/__tests__/visitor-test.ts

@@ -32,7 +32,7 @@ function checkVisitorFnArgs(ast: any, args: any, isEdited: boolean = false) {
   expect(parent).to.have.property(key);
 
   expect(path).to.be.an.instanceof(Array);
-  expect(path[path.length - 1]).to.equal(key);
+  expect(path.at(-1)).to.equal(key);
 
   expect(ancestors).to.be.an.instanceof(Array);
   expect(ancestors.length).to.equal(path.length - 1);

src/language/visitor.ts

@@ -296,7 +296,7 @@ export function visit(
 
   if (edits.length !== 0) {
     // New root
-    return edits[edits.length - 1][1];
+    return edits.at(-1)[1];
   }
 
   return root;

src/utilities/TypeInfo.ts

@@ -88,39 +88,27 @@ export class TypeInfo {
   }
 
   getType(): Maybe<GraphQLOutputType> {
-    if (this._typeStack.length > 0) {
-      return this._typeStack[this._typeStack.length - 1];
-    }
+    return this._typeStack.at(-1);
   }
 
   getParentType(): Maybe<GraphQLCompositeType> {
-    if (this._parentTypeStack.length > 0) {
-      return this._parentTypeStack[this._parentTypeStack.length - 1];
-    }
+    return this._parentTypeStack.at(-1);
   }
 
   getInputType(): Maybe<GraphQLInputType> {
-    if (this._inputTypeStack.length > 0) {
-      return this._inputTypeStack[this._inputTypeStack.length - 1];
-    }
+    return this._inputTypeStack.at(-1);
   }
 
   getParentInputType(): Maybe<GraphQLInputType> {
-    if (this._inputTypeStack.length > 1) {
-      return this._inputTypeStack[this._inputTypeStack.length - 2];
-    }
+    return this._inputTypeStack.at(-2);
   }
 
   getFieldDef(): Maybe<GraphQLField<unknown, unknown>> {
-    if (this._fieldDefStack.length > 0) {
-      return this._fieldDefStack[this._fieldDefStack.length - 1];
-    }
+    return this._fieldDefStack.at(-1);
   }
 
   getDefaultValue(): Maybe<unknown> {
-    if (this._defaultValueStack.length > 0) {
-      return this._defaultValueStack[this._defaultValueStack.length - 1];
-    }
+    return this._defaultValueStack.at(-1);
   }
 
   getDirective(): Maybe<GraphQLDirective> {

src/validation/rules/KnownDirectivesRule.ts

@@ -72,8 +72,8 @@ export function KnownDirectivesRule(
 function getDirectiveLocationForASTPath(
   ancestors: ReadonlyArray<ASTNode | ReadonlyArray<ASTNode>>,
 ): DirectiveLocation | undefined {
-  const appliedTo = ancestors[ancestors.length - 1];
-  invariant('kind' in appliedTo);
+  const appliedTo = ancestors.at(-1);
+  invariant(appliedTo != null && 'kind' in appliedTo);
 
   switch (appliedTo.kind) {
     case Kind.OPERATION_DEFINITION:
@@ -114,8 +114,8 @@ function getDirectiveLocationForASTPath(
     case Kind.INPUT_OBJECT_TYPE_EXTENSION:
       return DirectiveLocation.INPUT_OBJECT;
     case Kind.INPUT_VALUE_DEFINITION: {
-      const parentNode = ancestors[ancestors.length - 3];
-      invariant('kind' in parentNode);
+      const parentNode = ancestors.at(-3);
+      invariant(parentNode != null && 'kind' in parentNode);
       return parentNode.kind === Kind.INPUT_OBJECT_TYPE_DEFINITION
         ? DirectiveLocation.INPUT_FIELD_DEFINITION
         : DirectiveLocation.ARGUMENT_DEFINITION;