babel-plugin-replace-globals.js

/**
 * @format
 */

const t = require('@babel/types');
const babylon = require('@babel/parser');
const invariant = require('invariant');

const isGlobal = binding => !binding;

const isFlowDeclared = binding => t.isDeclareVariable(binding.path);

function isGlobalOrFlowDeclared(binding) {
  return isGlobal(binding) || isFlowDeclared(binding);
}

function isReplaceableGlobal(node, parent, scope, opts) {
  if (!t.isIdentifier(node)) {
    return false;
  }

  if (!Object.hasOwnProperty.call(opts, node.name)) {
    return false;
  }

  // Check that it's a global variable (not defined in any other place, or an object
  // property).
  return (
    isGlobalOrFlowDeclared(scope.getBinding(node.name)) &&
    !t.isMemberExpression(parent) &&
    !(t.isObjectProperty(parent) && parent.key === node)
  );
}

function getValue(node, opts) {
  invariant(
    opts.hasOwnProperty(node.name),
    `property ${node.name} should be present in plugin options`,
  );

  return opts[node.name];
}

function getAstFromValue(value) {
  switch (typeof value) {
    case 'string':
      return t.stringLiteral(value);
    case 'boolean':
      return t.booleanLiteral(value);
    case 'number':
      return t.numericLiteral(value);
    case 'undefined':
      return t.unaryExpression('void', t.numericLiteral(0), true);
  }

  return babylon.parseExpression(JSON.stringify(value));
}

module.exports = function replaceGlobal() {
  return {
    visitor: {
      Identifier(path, state) {
        if (
          isReplaceableGlobal(path.node, path.parent, path.scope, state.opts)
        ) {
          const value = getValue(path.node, state.opts);

          path.replaceWith(getAstFromValue(value));
        }
      },
    },
  };
};