Motions

A motion (aka migration) is what we call specific actions performed within a codemod. For example, updateBorderWidth or removeDeprecatedProps. They can be simply thought of as utility functions that are responsible for a single step within a complex codemod. It is not required to follow this pattern but they are highly recommended as a helpful design pattern to isolate more complicated parts of your codemod into discrete pieces.

Example:

function removeDeprecatedProps(j, source) {
  // Some logic here
}

Motions can then be applied from the main transform, just like any other function.

import { hasImportDeclaration } from '@hypermod/utils';
import removeDeprecatedProps from './motions/remove-deprecated-props';
import restructureImports from './motions/restructure-imports';

export default function transformer(file, { jscodeshift: j }, options) {
  const source = j(file.source);

  // Execute individual motions
  removeDeprecatedProps(j, source);
  restructureImports(j, source);

  return source.toSource(options.printOptions); // Writes modified AST to file
}

Each motion receives a reference to the AST (source) which it can then manipulate as required since the source variable is passed by reference.

Alternatively, you can use the utility function applyMotions to run motions in sequence.

import { applyMotions } from '@hypermod/utils';
import removeDeprecatedProps from './motions/remove-deprecated-props';
import restructureImports from './motions/restructure-imports';

export default function transformer(file, { jscodeshift: j }, options) {
  const source = j(file.source);

  // Execute a series of motions in order
  applyMotions(j, source, [removeDeprecatedProps, restructureImports]);

  return source.toSource(options.printOptions);
}