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📄 no-for-in-array

📊 Analysis Summary

Metric	Count
🔧 Functions	4
📦 Imports	4

📚 Table of Contents

• Default Export
• Imports
• Functions

🛠️ File Location:

📂 packages/eslint-plugin/src/rules/no-for-in-array.ts

📤 Default Export

export default createRule({ ... })

Property	Value
name	'no-for-in-array'
meta.type	'problem'
meta.docs.description	'Disallow iterating over an array with a for-in loop'
meta.docs.recommended	'recommended'
meta.docs.requiresTypeChecking	true
meta.messages.forInViolation	'For-in loops over arrays skips holes, returns indices as strings, and may visit the prototype chain or other enumera...
meta.schema	[]
defaultOptions	[]

Entry point: create — documented under Functions.

---

📦 Imports

Name	Source
createRule	../util
getConstrainedTypeAtLocation	../util
getParserServices	../util
getForStatementHeadLoc	../util/getForStatementHeadLoc

---

Functions

create(context: any): { ForInStatement(node: any): void; }

Parameters:

• context any

Returns: { ForInStatement(node: any): void; }

Calls:

• getParserServices (from ../util)
• services.program.getTypeChecker
• getConstrainedTypeAtLocation (from ../util)
• isArrayLike
• context.report
• getForStatementHeadLoc (from ../util/getForStatementHeadLoc)

Code

create(context) {
    return {
      ForInStatement(node): void {
        const services = getParserServices(context);
        const checker = services.program.getTypeChecker();

        const type = getConstrainedTypeAtLocation(services, node.right);

        if (isArrayLike(checker, type)) {
          context.report({
            loc: getForStatementHeadLoc(context.sourceCode, node),
            messageId: 'forInViolation',
          });
        }
      },
    };
  }

isArrayLike(checker: ts.TypeChecker, type: ts.Type): boolean

Parameters:

• checker ts.TypeChecker
• type ts.Type

Returns: boolean

Calls:

• isTypeRecurser
• t.getNumberIndexType
• hasArrayishLength

Code

function isArrayLike(checker: ts.TypeChecker, type: ts.Type): boolean {
  return isTypeRecurser(
    type,
    t => t.getNumberIndexType() != null && hasArrayishLength(checker, t),
  );
}

hasArrayishLength(checker: ts.TypeChecker, type: ts.Type): boolean

Parameters:

• checker ts.TypeChecker
• type ts.Type

Returns: boolean

Calls:

• type.getProperty
• tsutils.isTypeFlagSet
• checker.getTypeOfSymbol

Code

function hasArrayishLength(checker: ts.TypeChecker, type: ts.Type): boolean {
  const lengthProperty = type.getProperty('length');

  if (lengthProperty == null) {
    return false;
  }

  return tsutils.isTypeFlagSet(
    checker.getTypeOfSymbol(lengthProperty),
    ts.TypeFlags.NumberLike,
  );
}

isTypeRecurser(type: ts.Type, predicate: (t: ts.Type) => boolean): boolean

Parameters:

• type ts.Type
• predicate (t: ts.Type) => boolean

Returns: boolean

Calls:

• type.isUnionOrIntersection
• type.types.some
• isTypeRecurser
• predicate

Code

function isTypeRecurser(
  type: ts.Type,
  predicate: (t: ts.Type) => boolean,
): boolean {
  if (type.isUnionOrIntersection()) {
    return type.types.some(t => isTypeRecurser(t, predicate));
  }

  return predicate(type);
}

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