@dfinity/eslint-config-oisy-wallet/rules/use-nullish-checks.cjs

Shared ESLint configurations from the Oisy Wallet team

module.exports = {
  meta: {
    type: "suggestion",
    docs: {
      description: "Enforce the use of isNullish functions for nullish checks",
      category: "Best Practices",
      recommended: true,
    },
    messages: {
      isNullish:
        "Use isNullish() instead of direct variable check for nullish checks.",
      nonNullish:
        "Use nonNullish() instead of direct variable check for nullish checks.",
    },
    fixable: "code",
    schema: [],
  },

  create: (context) => {
    const binaryCheck = (node) => {
      if (node.type === "BinaryExpression") {
        return (
          (node.operator === "===" || node.operator === "!==") &&
          ((node.right.type === "Identifier" &&
            node.right.name === "undefined") ||
            (node.right.type === "Literal" && node.right.value === null))
        );
      }
    };

    const binaryReportCheck = (node) => {
      context.report({
        node,
        messageId: node.operator === "===" ? "isNullish" : "nonNullish",
        fix: (fixer) =>
          fixer.replaceText(
            node,
            `${node.operator === "===" ? "isNullish" : "nonNullish"}(${context.sourceCode.getText(node.left)})`,
          ),
      });
    };

    return {
      BinaryExpression: (node) => {
        if (binaryCheck(node)) {
          binaryReportCheck(node);
        }
      },
    };
  },
};