babel/packages/babel-helper-explode-assignable-expression/src/index.js

/* @flow */

import type { Scope } from "babel-traverse";
import * as t from "babel-types";

function getObjRef(node, nodes, file, scope) {
  let ref;
  if (t.isIdentifier(node)) {
    if (scope.hasBinding(node.name)) {
      // this variable is declared in scope so we can be 100% sure
      // that evaluating it multiple times wont trigger a getter
      // or something else
      return node;
    } else {
      // could possibly trigger a getter so we need to only evaluate
      // it once
      ref = node;
    }
  } else if (t.isMemberExpression(node)) {
    ref = node.object;

    if (t.isIdentifier(ref) && scope.hasBinding(ref.name)) {
      // the object reference that we need to save is locally declared
      // so as per the previous comment we can be 100% sure evaluating
      // it multiple times will be safe
      return ref;
    }
  } else {
    throw new Error(`We can't explode this node type ${node.type}`);
  }

  let temp = scope.generateUidIdentifierBasedOnNode(ref);
  nodes.push(t.variableDeclaration("var", [
    t.variableDeclarator(temp, ref)
  ]));
  return temp;
}

function getPropRef(node, nodes, file, scope) {
  let prop = node.property;
  let key = t.toComputedKey(node, prop);
  if (t.isLiteral(key)) return key;

  let temp = scope.generateUidIdentifierBasedOnNode(prop);
  nodes.push(t.variableDeclaration("var", [
    t.variableDeclarator(temp, prop)
  ]));
  return temp;
}

export default function (
  node: Object,
  nodes: Array<Object>,
  file,
  scope: Scope,
  allowedSingleIdent?: boolean,
): {
  uid: Object;
  ref: Object;
} {
  let obj;
  if (t.isIdentifier(node) && allowedSingleIdent) {
    obj = node;
  } else {
    obj = getObjRef(node, nodes, file, scope);
  }

  let ref, uid;

  if (t.isIdentifier(node)) {
    ref = node;
    uid = obj;
  } else {
    let prop = getPropRef(node, nodes, file, scope);
    let computed = node.computed || t.isLiteral(prop);
    uid = ref = t.memberExpression(obj, prop, computed);
  }

  return {
    uid: uid,
    ref: ref
  };
}