match-ast

match-ast

Collection of helper functions to verify a AST tree structure.

Usage

Type matchers

Example: verify if a tree represents a JSON.stringify() call

const {
  isCallExpression,
  isMemberExpression,
  isIdentifier
} = require("match-ast");

// Check if the tree represents a `JSON.stringify()` call.
const isJsonStringify = isCallExpression({
  callee: isMemberExpression({
    object: isIdentifier("JSON"),
    property: isIdentifier("stringify")
  })
});

Most functions are named isSomething where Something is the type of the node (i.e. isIdentifier checks if node.type === "Identifier"). They accept a single argument: an object where keys represent the property of a node and the value is a matcher for that property.

The accepted matchers are: a matcher function, primitive values, arrays or functions.

Calling a function with no arguments means it will only assert its type and none of the properties. For types with no properties (i.e. ThisExpression), arguments are ignored.

For nodes with only a single property (i.e. Identifier with property name), you can pass directly the matcher for that property, so you don't have to pass an object with a single property. For example, isIdentifier("foo") is equivalent to isIdentifier({ name: "foo" }).

Passing extra properties to a matcher will make it always return false:

// check() will always return false since there's no `name` property in CallExpression
const check = isCallExpression({ name: "foo" });

Other matchers

either

For cases where a node can be one of many values:

const { either, isIdentifier, isMemberExpression } = require("match-ast");

// Check if the three is a `JSON.stringify()` or `stringify()` call
const isStringify = isCallExpression({
  callee: either(
    isMemberExpression({
      object: isIdentifier("JSON"),
      property: isIdentifier("stringify")
    }),
    isIdentifier("stringify")
  )
});

Credits

This library consists of helper functions automatically generated on top of the excellent @babel/types definitions.