jsx-ast-utils

What is jsx-ast-utils?

The jsx-ast-utils package provides utilities for working with the Abstract Syntax Tree (AST) of JSX elements. It is commonly used in the development of linting rules and tools that analyze or transform JSX code.

What are jsx-ast-utils's main functionalities?

Element and attribute extraction

This feature allows you to extract properties and their literal values from a JSX element. It is useful when analyzing components for specific attribute values.

const { getProp, getLiteralPropValue } = require('jsx-ast-utils');
const JSXElement = ...; // some JSX element AST node
const prop = getProp(JSXElement, 'href');
const value = getLiteralPropValue(prop);

Event handler detection

This feature helps in detecting event handlers on JSX elements. It can be used to ensure that interactive elements have appropriate event handlers for accessibility.

const { getProp, elementType } = require('jsx-ast-utils');
const JSXElement = ...; // some JSX element AST node
const type = elementType(JSXElement);
const onClickProp = getProp(JSXElement, 'onClick');
const isButtonWithOnClick = type === 'button' && onClickProp !== undefined;

Checking for children

These utilities allow you to check if a JSX element has any children or if every child meets a specific condition. This can be used to enforce content structure within components.

const { hasAnyChildren, hasEveryChild } = require('jsx-ast-utils');
const JSXElement = ...; // some JSX element AST node
const hasChildren = hasAnyChildren(JSXElement);
const hasSpecificChildren = hasEveryChild(JSXElement, child => child.type === 'JSXText');

Other packages similar to jsx-ast-utils

babel-plugin-jsx

This package is a Babel plugin that allows for transformation of JSX syntax. It provides similar AST manipulation capabilities but is more focused on compiling JSX to JavaScript rather than analyzing or linting.

eslint-plugin-react

This package includes a collection of ESLint rules for React and JSX. It uses AST analysis to enforce best practices and coding standards. While it does not provide low-level AST utilities like jsx-ast-utils, it serves a similar purpose in the context of linting and code quality.

react-docgen

react-docgen is a CLI and toolkit for extracting information from React component files for documentation generation. It analyzes the AST to gather prop types, default values, and component descriptions. It is similar in that it analyzes JSX, but it is more specialized for documentation purposes.

README

jsx-ast-utils

AST utility module for statically analyzing JSX.

Installation

$ npm i jsx-ast-utils --save

Usage

This is a utility module to evaluate AST objects for JSX syntax. This can be super useful when writing linting rules for JSX code. It was originally in the code for eslint-plugin-jsx-a11y, however I thought it could be useful to be extracted and maintained separately so you could write new interesting rules to statically analyze JSX.

ESLint example

import { hasProp } from 'jsx-ast-utils';
// OR: var hasProp = require('jsx-ast-utils').hasProp;
// OR: const hasProp = require('jsx-ast-utils/hasProp');
// OR: import hasProp from 'jsx-ast-utils/hasProp';

module.exports = context => ({
  JSXOpeningElement: node => {
    const onChange = hasProp(node.attributes, 'onChange');

    if (onChange) {
      context.report({
        node,
        message: `No onChange!`
      });
    }
  }
});

API

AST Resources

1. JSX spec
2. JS spec

hasProp

hasProp(props, prop, options);

Returns boolean indicating whether an prop exists as an attribute on a JSX element node.

Props

Object - The attributes on the visited node. (Usually node.attributes).

Prop

String - A string representation of the prop you want to check for existence.

Options

Object - An object representing options for existence checking

1. ignoreCase - automatically set to true.
2. spreadStrict - automatically set to true. This means if spread operator exists in props, it will assume the prop you are looking for is not in the spread. Example: <div {...props} /> looking for specific prop here will return false if spreadStrict is true.

---

### hasAnyProp ```js hasAnyProp(props, prop, options); ``` Returns a boolean indicating if **any** of props in `prop` argument exist on the node.

Props

Object - The attributes on the visited node. (Usually node.attributes).

Prop

Array - An array of strings representing the props you want to check for existence.

Options

Object - An object representing options for existence checking

1. ignoreCase - automatically set to true.
2. spreadStrict - automatically set to true. This means if spread operator exists in props, it will assume the prop you are looking for is not in the spread. Example: <div {...props} /> looking for specific prop here will return false if spreadStrict is true.

---

### hasEveryProp ```js hasEveryProp(props, prop, options); ``` Returns a boolean indicating if **all** of props in `prop` argument exist on the node.

Props

Object - The attributes on the visited node. (Usually node.attributes).

Prop

Array - An array of strings representing the props you want to check for existence.

Options

Object - An object representing options for existence checking

1. ignoreCase - automatically set to true.
2. spreadStrict - automatically set to true. This means if spread operator exists in props, it will assume the prop you are looking for is not in the spread. Example: <div {...props} /> looking for specific prop here will return false if spreadStrict is true.

---

### getProp ```js getProp(props, prop, options); ``` Returns the JSXAttribute itself or undefined, indicating the prop is not present on the JSXOpeningElement.

Props

Object - The attributes on the visited node. (Usually node.attributes).

Prop

String - A string representation of the prop you want to check for existence.

Options

Object - An object representing options for existence checking

1. ignoreCase - automatically set to true.

---

### elementType ```js elementType(node) ``` Returns the tagName associated with a JSXElement.

Node

Object - The visited JSXElement node object.

---

### getPropValue ```js getPropValue(prop); ``` Returns the value of a given attribute. Different types of attributes have their associated values in different properties on the object.

This function should return the most closely associated value with the intention of the JSX.

Prop

Object - The JSXAttribute collected by AST parser.

---

### getLiteralPropValue ```js getLiteralPropValue(prop); ``` Returns the value of a given attribute. Different types of attributes have their associated values in different properties on the object.

This function should return a value only if we can extract a literal value from its attribute (i.e. values that have generic types in JavaScript - strings, numbers, booleans, etc.)

Prop

Object - The JSXAttribute collected by AST parser.

---

### propName ```js propName(prop); ``` Returns the name associated with a JSXAttribute. For example, given `

` and the JSXAttribute for `foo`, this will return the string `"foo"`.

Prop

Object - The JSXAttribute collected by AST parser.