eslint-template-visitor

2.3.2 verified Sat Apr 25 auth: no javascript

Simplify ESLint rule creation by visiting AST node templates instead of manually inspecting ESTree nodes. v2.3.2 supports ESLint >=7 and uses @babel/eslint-parser behind the scenes for template parsing. It offers a declarative API with template literals, variables, spread variables, and variable declaration variables. Maintained by futpib, with regular releases and active development. Differentiates from other template-based tools by integrating directly with ESLint's visitor pattern.

Common errors

error TypeError: templates.template is not a function ↓

cause Calling template on the default export directly without calling eslintTemplateVisitor first.

fix

Call eslintTemplateVisitor() to get the templates object, then use templates.template.

error Error: Template must have exactly one top-level node ↓

cause Template string contains multiple top-level statements or expressions.

fix

Wrap the template in a block or ensure only one top-level node.

error Cannot find module '@babel/eslint-parser' ↓

cause @babel/eslint-parser is required as a dependency since v2.3.0 but not installed.

fix

Install @babel/eslint-parser: npm install --save-dev @babel/eslint-parser

error TypeError: context.getMatch is not a function ↓

cause Accessing getMatch incorrectly (e.g., on context instead of template context).

fix

Use substrCallTemplate.context.getMatch(objVar) not context.getMatch.

error ReferenceError: eslintTemplateVisitor is not defined ↓

cause Forgetting to import/require the module.

fix

Add const eslintTemplateVisitor = require('eslint-template-visitor'); or import statement.

Warnings

breaking Upgraded parser from babel-eslint to @babel/eslint-parser in v2.3.0. Existing templates that relied on babel-eslint-specific behavior may break. ↓

fix Update parser options if needed, ensure @babel/eslint-parser is installed as a direct dependency.

deprecated The old babel-eslint parser is deprecated; v2.3.0 switched to @babel/eslint-parser. ↓

fix Upgrade to v2.3.0 or later to avoid deprecated babel-eslint.

gotcha Template cannot have more than one top-level node. Throws an error in v2.1.0+. ↓

fix Ensure template string contains exactly one top-level AST node.

gotcha Variable declaration variable (variableDeclarationVariable) must be used in place of the declaration keyword (const/let/var), not the entire declaration node. ↓

fix Use ${variableDeclarationVariable} x = y; instead of ${variableDeclarationVariable} x = y; with wrong placement.

gotcha Spread variable matches an array of nodes, not a single node. Mistaking it for a regular variable leads to incorrect type errors. ↓

fix Use templates.variable() for a single node match, templates.spreadVariable() for an array.

breaking Removal of support for ESLint <7.0.0. Peer dependency requires eslint >=7. ↓

fix Upgrade ESLint to version 7 or later.

Install

npm install eslint-template-visitor

yarn add eslint-template-visitor

pnpm add eslint-template-visitor

Imports

default

wrong

const { eslintTemplateVisitor } = require('eslint-template-visitor');

correct

import eslintTemplateVisitor from 'eslint-template-visitor';

Default export is the factory function. Named import is incorrect.

default (require)

wrong

const { template } = require('eslint-template-visitor');

correct

const eslintTemplateVisitor = require('eslint-template-visitor');

CommonJS require returns the default export directly.

template (after calling factory)
wrong
```
const { template } = eslintTemplateVisitor();
```
correct
```
const templates = eslintTemplateVisitor(); const { template } = templates;
```
template is a method on the object returned by the factory function, not a named export of the module.

Quickstart

ESLint rule using template visitor to detect and optionally fix .substr() calls.

const eslintTemplateVisitor = require('eslint-template-visitor');
const templates = eslintTemplateVisitor();

const objVar = templates.variable();
const argVar = templates.spreadVariable();
const substrCallTemplate = templates.template`${objVar}.substr(${argVar})`;

module.exports = {
  meta: {
    type: 'suggestion',
    docs: {
      description: 'Prefer String#slice() over String#substr()',
    },
    fixable: 'code',
  },
  create(context) {
    return templates.visitor({
      [substrCallTemplate](node) {
        const objectNode = substrCallTemplate.context.getMatch(objVar);
        const argumentNodes = substrCallTemplate.context.getMatch(argVar);
        const problem = {
          node,
          message: 'Prefer `String#slice()` over `String#substr()`.',
        };
        if (argumentNodes.length === 0) {
          problem.fix = fixer => fixer.replaceText(node, context.getSourceCode().getText(objectNode) + '.slice()');
        }
        context.report(problem);
      },
    });
  },
};