react app

react-app/node_modules/jstransform/visitors/es6-arrow-function-visitors.js

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+/**
+ * Copyright 2013 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*global exports:true*/
+
+/**
+ * Desugars ES6 Arrow functions to ES3 function expressions.
+ * If the function contains `this` expression -- automatically
+ * binds the function to current value of `this`.
+ *
+ * Single parameter, simple expression:
+ *
+ * [1, 2, 3].map(x => x * x);
+ *
+ * [1, 2, 3].map(function(x) { return x * x; });
+ *
+ * Several parameters, complex block:
+ *
+ * this.users.forEach((user, idx) => {
+ *   return this.isActive(idx) && this.send(user);
+ * });
+ *
+ * this.users.forEach(function(user, idx) {
+ *   return this.isActive(idx) && this.send(user);
+ * }.bind(this));
+ *
+ */
+var restParamVisitors = require('./es6-rest-param-visitors');
+var destructuringVisitors = require('./es6-destructuring-visitors');
+
+var Syntax = require('esprima-fb').Syntax;
+var utils = require('../src/utils');
+
+/**
+ * @public
+ */
+function visitArrowFunction(traverse, node, path, state) {
+  var notInExpression = (path[0].type === Syntax.ExpressionStatement);
+
+  // Wrap a function into a grouping operator, if it's not
+  // in the expression position.
+  if (notInExpression) {
+    utils.append('(', state);
+  }
+
+  utils.append('function', state);
+  renderParams(traverse, node, path, state);
+
+  // Skip arrow.
+  utils.catchupWhiteSpace(node.body.range[0], state);
+
+  var renderBody = node.body.type == Syntax.BlockStatement
+    ? renderStatementBody
+    : renderExpressionBody;
+
+  path.unshift(node);
+  renderBody(traverse, node, path, state);
+  path.shift();
+
+  // Bind the function only if `this` value is used
+  // inside it or inside any sub-expression.
+  var containsBindingSyntax =
+    utils.containsChildMatching(node.body, function(node) {
+      return node.type === Syntax.ThisExpression
+             || (node.type === Syntax.Identifier
+                 && node.name === "super");
+    });
+
+  if (containsBindingSyntax) {
+    utils.append('.bind(this)', state);
+  }
+
+  utils.catchupWhiteSpace(node.range[1], state);
+
+  // Close wrapper if not in the expression.
+  if (notInExpression) {
+    utils.append(')', state);
+  }
+
+  return false;
+}
+
+function renderParams(traverse, node, path, state) {
+  // To preserve inline typechecking directives, we
+  // distinguish between parens-free and paranthesized single param.
+  if (isParensFreeSingleParam(node, state) || !node.params.length) {
+    utils.append('(', state);
+  }
+  if (node.params.length !== 0) {
+    path.unshift(node);
+    traverse(node.params, path, state);
+    path.unshift();
+  }
+  utils.append(')', state);
+}
+
+function isParensFreeSingleParam(node, state) {
+  return node.params.length === 1 &&
+    state.g.source[state.g.position] !== '(';
+}
+
+function renderExpressionBody(traverse, node, path, state) {
+  // Wrap simple expression bodies into a block
+  // with explicit return statement.
+  utils.append('{', state);
+
+  // Special handling of rest param.
+  if (node.rest) {
+    utils.append(
+      restParamVisitors.renderRestParamSetup(node, state),
+      state
+    );
+  }
+
+  // Special handling of destructured params.
+  destructuringVisitors.renderDestructuredComponents(
+    node,
+    utils.updateState(state, {
+      localScope: {
+        parentNode: state.parentNode,
+        parentScope: state.parentScope,
+        identifiers: state.identifiers,
+        tempVarIndex: 0
+      }
+    })
+  );
+
+  utils.append('return ', state);
+  renderStatementBody(traverse, node, path, state);
+  utils.append(';}', state);
+}
+
+function renderStatementBody(traverse, node, path, state) {
+  traverse(node.body, path, state);
+  utils.catchup(node.body.range[1], state);
+}
+
+visitArrowFunction.test = function(node, path, state) {
+  return node.type === Syntax.ArrowFunctionExpression;
+};
+
+exports.visitorList = [
+  visitArrowFunction
+];
+