diff --git a/src/jsutils/suggestionList.js b/src/jsutils/suggestionList.js
index 88ef53f092..7e6bcbeb4a 100644
--- a/src/jsutils/suggestionList.js
+++ b/src/jsutils/suggestionList.js
@@ -16,13 +16,12 @@ export default function suggestionList(
   options: $ReadOnlyArray<string>,
 ): Array<string> {
   const optionsByDistance = Object.create(null);
-  const oLength = options.length;
   const inputThreshold = input.length / 2;
-  for (let i = 0; i < oLength; i++) {
-    const distance = lexicalDistance(input, options[i]);
-    const threshold = Math.max(inputThreshold, options[i].length / 2, 1);
+  for (const option of options) {
+    const distance = lexicalDistance(input, option);
+    const threshold = Math.max(inputThreshold, option.length / 2, 1);
     if (distance <= threshold) {
-      optionsByDistance[options[i]] = distance;
+      optionsByDistance[option] = distance;
     }
   }
   return Object.keys(optionsByDistance).sort(
diff --git a/src/utilities/astFromValue.js b/src/utilities/astFromValue.js
index 0ba2f323fc..dd805141d2 100644
--- a/src/utilities/astFromValue.js
+++ b/src/utilities/astFromValue.js
@@ -84,9 +84,8 @@ export function astFromValue(value: mixed, type: GraphQLInputType): ?ValueNode {
     if (value === null || typeof value !== 'object') {
       return null;
     }
-    const fields = objectValues(type.getFields());
     const fieldNodes = [];
-    for (const field of fields) {
+    for (const field of objectValues(type.getFields())) {
       const fieldValue = astFromValue(value[field.name], field.type);
       if (fieldValue) {
         fieldNodes.push({
diff --git a/src/utilities/getOperationAST.js b/src/utilities/getOperationAST.js
index 6c09e17b37..2e8dacf0ee 100644
--- a/src/utilities/getOperationAST.js
+++ b/src/utilities/getOperationAST.js
@@ -23,8 +23,7 @@ export function getOperationAST(
   operationName: ?string,
 ): ?OperationDefinitionNode {
   let operation = null;
-  for (let i = 0; i < documentAST.definitions.length; i++) {
-    const definition = documentAST.definitions[i];
+  for (const definition of documentAST.definitions) {
     if (definition.kind === Kind.OPERATION_DEFINITION) {
       if (!operationName) {
         // If no operation name was provided, only return an Operation if there
diff --git a/src/utilities/schemaPrinter.js b/src/utilities/schemaPrinter.js
index 792c692fb3..965e9bb192 100644
--- a/src/utilities/schemaPrinter.js
+++ b/src/utilities/schemaPrinter.js
@@ -339,11 +339,11 @@ function printDescription(
 
 function printDescriptionWithComments(lines, indentation, firstInBlock) {
   let description = indentation && !firstInBlock ? '\n' : '';
-  for (let i = 0; i < lines.length; i++) {
-    if (lines[i] === '') {
+  for (const line of lines) {
+    if (line === '') {
       description += indentation + '#\n';
     } else {
-      description += indentation + '# ' + lines[i] + '\n';
+      description += indentation + '# ' + line + '\n';
     }
   }
   return description;
diff --git a/src/utilities/valueFromAST.js b/src/utilities/valueFromAST.js
index 6b797f9eca..40f3c58d24 100644
--- a/src/utilities/valueFromAST.js
+++ b/src/utilities/valueFromAST.js
@@ -86,9 +86,8 @@ export function valueFromAST(
     const itemType = type.ofType;
     if (valueNode.kind === Kind.LIST) {
       const coercedValues = [];
-      const itemNodes = valueNode.values;
-      for (let i = 0; i < itemNodes.length; i++) {
-        if (isMissingVariable(itemNodes[i], variables)) {
+      for (const itemNode of valueNode.values) {
+        if (isMissingVariable(itemNode, variables)) {
           // If an array contains a missing variable, it is either coerced to
           // null or if the item type is non-null, it considered invalid.
           if (isNonNullType(itemType)) {
@@ -96,7 +95,7 @@ export function valueFromAST(
           }
           coercedValues.push(null);
         } else {
-          const itemValue = valueFromAST(itemNodes[i], itemType, variables);
+          const itemValue = valueFromAST(itemNode, itemType, variables);
           if (isInvalid(itemValue)) {
             return; // Invalid: intentionally return no value.
           }
@@ -118,9 +117,7 @@ export function valueFromAST(
     }
     const coercedObj = Object.create(null);
     const fieldNodes = keyMap(valueNode.fields, field => field.name.value);
-    const fields = objectValues(type.getFields());
-    for (let i = 0; i < fields.length; i++) {
-      const field = fields[i];
+    for (const field of objectValues(type.getFields())) {
       const fieldNode = fieldNodes[field.name];
       if (!fieldNode || isMissingVariable(fieldNode.value, variables)) {
         if (field.defaultValue !== undefined) {
diff --git a/src/validation/ValidationContext.js b/src/validation/ValidationContext.js
index 9bdc6ae572..baed70b4c2 100644
--- a/src/validation/ValidationContext.js
+++ b/src/validation/ValidationContext.js
@@ -97,8 +97,7 @@ export class ASTValidationContext {
       const setsToVisit: Array<SelectionSetNode> = [node];
       while (setsToVisit.length !== 0) {
         const set = setsToVisit.pop();
-        for (let i = 0; i < set.selections.length; i++) {
-          const selection = set.selections[i];
+        for (const selection of set.selections) {
           if (selection.kind === Kind.FRAGMENT_SPREAD) {
             spreads.push(selection);
           } else if (selection.selectionSet) {
@@ -121,9 +120,8 @@ export class ASTValidationContext {
       const nodesToVisit: Array<SelectionSetNode> = [operation.selectionSet];
       while (nodesToVisit.length !== 0) {
         const node = nodesToVisit.pop();
-        const spreads = this.getFragmentSpreads(node);
-        for (let i = 0; i < spreads.length; i++) {
-          const fragName = spreads[i].name.value;
+        for (const spread of this.getFragmentSpreads(node)) {
+          const fragName = spread.name.value;
           if (collectedNames[fragName] !== true) {
             collectedNames[fragName] = true;
             const fragment = this.getFragment(fragName);
@@ -212,12 +210,8 @@ export class ValidationContext extends ASTValidationContext {
     let usages = this._recursiveVariableUsages.get(operation);
     if (!usages) {
       usages = this.getVariableUsages(operation);
-      const fragments = this.getRecursivelyReferencedFragments(operation);
-      for (let i = 0; i < fragments.length; i++) {
-        Array.prototype.push.apply(
-          usages,
-          this.getVariableUsages(fragments[i]),
-        );
+      for (const frag of this.getRecursivelyReferencedFragments(operation)) {
+        usages = usages.concat(this.getVariableUsages(frag));
       }
       this._recursiveVariableUsages.set(operation, usages);
     }
diff --git a/src/validation/rules/NoFragmentCycles.js b/src/validation/rules/NoFragmentCycles.js
index 993a82253d..a9234a42aa 100644
--- a/src/validation/rules/NoFragmentCycles.js
+++ b/src/validation/rules/NoFragmentCycles.js
@@ -57,8 +57,7 @@ export function NoFragmentCycles(context: ASTValidationContext): ASTVisitor {
 
     spreadPathIndexByName[fragmentName] = spreadPath.length;
 
-    for (let i = 0; i < spreadNodes.length; i++) {
-      const spreadNode = spreadNodes[i];
+    for (const spreadNode of spreadNodes) {
       const spreadName = spreadNode.name.value;
       const cycleIndex = spreadPathIndexByName[spreadName];