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📄 no-duplicate-enum-values

📊 Analysis Summary

Metric	Count
🔧 Functions	6
📦 Imports	3

📚 Table of Contents

• Default Export
• Imports
• Functions

🛠️ File Location:

📂 packages/eslint-plugin/src/rules/no-duplicate-enum-values.ts

📤 Default Export

export default createRule({ ... })

Property	Value
name	'no-duplicate-enum-values'
meta.type	'problem'
meta.docs.description	'Disallow duplicate enum member values'
meta.docs.recommended	'recommended'
meta.hasSuggestions	false
meta.messages.duplicateValue	'Duplicate enum member value {{value}}.'
meta.schema	[]
defaultOptions	[]

Entry point: create — documented under Functions.

---

📦 Imports

Name	Source
TSESTree	@typescript-eslint/utils
AST_NODE_TYPES	@typescript-eslint/utils
createRule	../util

---

Functions

create(context: any): { TSEnumDeclaration(node: TSESTree.TSEnumDeclaration): void…

Parameters:

• context any

Returns: { TSEnumDeclaration(node: TSESTree.TSEnumDeclaration): void; }

Calls:

• ['-', '+'].includes
• isStringLiteral
• isNumberLiteral
• isSupportedUnary
• Number
• getMemberValue
• Number.isNaN
• isStaticTemplateLiteral
• enumMembers.forEach
• seenValues.some
• Object.is
• context.report
• seenValues.push

Code

create(context) {
    function isStringLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.StringLiteral {
      return (
        node.type === AST_NODE_TYPES.Literal && typeof node.value === 'string'
      );
    }

    function isNumberLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.NumberLiteral {
      return (
        node.type === AST_NODE_TYPES.Literal && typeof node.value === 'number'
      );
    }

    function isSupportedUnary(
      node: TSESTree.Expression,
    ): node is TSESTree.UnaryExpression {
      return (
        node.type === AST_NODE_TYPES.UnaryExpression &&
        ['-', '+'].includes(node.operator)
      );
    }

    function isStaticTemplateLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.TemplateLiteral {
      return (
        node.type === AST_NODE_TYPES.TemplateLiteral &&
        node.expressions.length === 0 &&
        node.quasis.length === 1
      );
    }

    function getMemberValue(
      initializer: TSESTree.Expression,
    ): number | string | undefined {
      switch (true) {
        case isStringLiteral(initializer):
        case isNumberLiteral(initializer):
          return initializer.value;
        case isSupportedUnary(initializer): {
          const inner = Number(getMemberValue(initializer.argument));
          if (Number.isNaN(inner)) {
            return undefined;
          }

          return initializer.operator === '-' ? -inner : inner;
        }
        case isStaticTemplateLiteral(initializer):
          return initializer.quasis[0].value.cooked ?? undefined;
        default:
          return undefined;
      }
    }

    return {
      TSEnumDeclaration(node: TSESTree.TSEnumDeclaration): void {
        const enumMembers = node.body.members;
        const seenValues: (number | string)[] = [];

        enumMembers.forEach(member => {
          if (member.initializer == null) {
            return;
          }

          const value = getMemberValue(member.initializer);
          if (value == null) {
            return;
          }

          const isAlreadyPresent = seenValues.some(seenValue =>
            Object.is(seenValue, value),
          );
          if (isAlreadyPresent) {
            context.report({
              node: member,
              messageId: 'duplicateValue',
              data: {
                value,
              },
            });
          } else {
            seenValues.push(value);
          }
        });
      },
    };
  }

Internal helpers

Declared inside another function in this file.

isStringLiteral(node: TSESTree.Expression): node is TSESTree.StringLiteral

Parameters:

• node TSESTree.Expression

Returns: node is TSESTree.StringLiteral

Code

function isStringLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.StringLiteral {
      return (
        node.type === AST_NODE_TYPES.Literal && typeof node.value === 'string'
      );
    }

isNumberLiteral(node: TSESTree.Expression): node is TSESTree.NumberLiteral

Parameters:

• node TSESTree.Expression

Returns: node is TSESTree.NumberLiteral

Code

function isNumberLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.NumberLiteral {
      return (
        node.type === AST_NODE_TYPES.Literal && typeof node.value === 'number'
      );
    }

isSupportedUnary(node: TSESTree.Expression): node is TSESTree.UnaryExpression

Parameters:

• node TSESTree.Expression

Returns: node is TSESTree.UnaryExpression

Calls:

• ['-', '+'].includes

Code

function isSupportedUnary(
      node: TSESTree.Expression,
    ): node is TSESTree.UnaryExpression {
      return (
        node.type === AST_NODE_TYPES.UnaryExpression &&
        ['-', '+'].includes(node.operator)
      );
    }

isStaticTemplateLiteral(node: TSESTree.Expression): node is TSESTree.TemplateLiteral

Parameters:

• node TSESTree.Expression

Returns: node is TSESTree.TemplateLiteral

Code

function isStaticTemplateLiteral(
      node: TSESTree.Expression,
    ): node is TSESTree.TemplateLiteral {
      return (
        node.type === AST_NODE_TYPES.TemplateLiteral &&
        node.expressions.length === 0 &&
        node.quasis.length === 1
      );
    }

getMemberValue(initializer: TSESTree.Expression): number | string | undefined

Parameters:

• initializer TSESTree.Expression

Returns: number | string | undefined

Calls:

• isStringLiteral
• isNumberLiteral
• isSupportedUnary
• Number
• getMemberValue
• Number.isNaN
• isStaticTemplateLiteral

Code

function getMemberValue(
      initializer: TSESTree.Expression,
    ): number | string | undefined {
      switch (true) {
        case isStringLiteral(initializer):
        case isNumberLiteral(initializer):
          return initializer.value;
        case isSupportedUnary(initializer): {
          const inner = Number(getMemberValue(initializer.argument));
          if (Number.isNaN(inner)) {
            return undefined;
          }

          return initializer.operator === '-' ? -inner : inner;
        }
        case isStaticTemplateLiteral(initializer):
          return initializer.quasis[0].value.cooked ?? undefined;
        default:
          return undefined;
      }
    }

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