eslint-template-visitor

ESLint Template Visitor

Simplify eslint rules by visiting templates

Install

npm install eslint-template-visitor

# or

yarn add eslint-template-visitor

Showcase

+const eslintTemplateVisitor = require('eslint-template-visitor');
+
+const templates = eslintTemplateVisitor();
+
+const objectVariable = templates.variable();
+const argumentsVariable = templates.spreadVariable();
+
+const substrCallTemplate = templates.template`${objectVariable}.substr(${argumentsVariable})`;

 const create = context => {
 	const sourceCode = context.getSourceCode();

-	return {
-		CallExpression(node) {
-			if (node.callee.type !== 'MemberExpression'
-				|| node.callee.property.type !== 'Identifier'
-				|| node.callee.property.name !== 'substr'
-			) {
-				return;
-			}
-
-			const objectNode = node.callee.object;
+	return templates.visitor({
+		[substrCallTemplate](node) {
+			const objectNode = substrCallTemplate.context.getMatch(objectVariable);
+			const argumentNodes = substrCallTemplate.context.getMatch(argumentsVariable);

 			const problem = {
 				node,
 				message: 'Prefer `String#slice()` over `String#substr()`.',
 			};

-			const canFix = node.arguments.length === 0;
+			const canFix = argumentNodes.length === 0;

 			if (canFix) {
 				problem.fix = fixer => fixer.replaceText(node, sourceCode.getText(objectNode) + '.slice()');
 			}

 			context.report(problem);
 		},
-	};
+	});
 };

See examples for more.

API

eslintTemplateVisitor(options?)

Craete a template visitor.

Example:

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

const templates = eslintTemplateVisitor();

options

Type: object

parserOptions

Options for the template parser. Passed down to espree.

Example:

const templates = eslintTemplateVisitor({
	parserOptions: {
		ecmaVersion: 2018,
	},
});

templates.variable()

Create a variable to be used in a template. Such a variable can match exactly one AST node.

templates.spreadVariable()

Create a spread variable. Spread variable can match an array of AST nodes.

This is useful for matching a number of arguments in a call or a number of statements in a block.

templates.variableDeclarationVariable()

Create a variable declaration variable. Variable declaration variable can match any type of variable declaration node.

This is useful for matching any variable declaration, be it const, let or var.

templates.template tag

Creates a template possibly containing variables.

Example:

const objectVariable = templates.variable();
const argumentsVariable = templates.spreadVariable();

const substrCallTemplate = templates.template`${objectVariable}.substr(${argumentsVariable})`;

const create = () => templates.visitor({
	[substrCallTemplate](node) {
		// `node` here is the matching `.substr` call (i.e. `CallExpression`)
	}
});

templates.visitor({ /* visitors */ })

Used to merge template visitors with common ESLint visitors.

Example:

const create = () => templates.visitor({
	[substrCallTemplate](node) {
		// Template visitor
	},

	FunctionDeclaration(node) {
		// Simple node type visitor
	},

	'IfStatement > BlockStatement'(node) {
		// ESLint selector visitor
	},
});

template.context

A template match context. This property is defined only within a visitor call (in other words, only when working on a matching node).

Example:

const create = () => templates.visitor({
	[substrCallTemplate](node) {
		// `substrCallTemplate.context` can be used here
	},

	FunctionDeclaration(node) {
		// `substrCallTemplate.context` is not defined here, and it does not make sense to use it here,
		// since we `substrCallTemplate` did not match an AST node.
	},
});

template.context.getMatch(variable)

Used to get a match for a variable.

Example:

const objectVariable = templates.variable();
const argumentsVariable = templates.spreadVariable();

const substrCallTemplate = templates.template`${objectVariable}.substr(${argumentsVariable})`;

const create = () => templates.visitor({
	[substrCallTemplate](node) {
		const objectNode = substrCallTemplate.context.getMatch(objectVariable);

		// For example, let's check if `objectNode` is an `Identifier`: `objectNode.type === 'Identifier'`

		const argumentNodes = substrCallTemplate.context.getMatch(argumentsVariable);

		// `Array.isArray(argumentNodes) === true`
	},
});