flow like the river

VISUALIZACION/node_modules/regenerator-transform/src/hoist.js

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+/**
+ * Copyright (c) 2014, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * https://raw.github.com/facebook/regenerator/master/LICENSE file. An
+ * additional grant of patent rights can be found in the PATENTS file in
+ * the same directory.
+ */
+
+import * as t from "babel-types";
+import * as util from "./util";
+let hasOwn = Object.prototype.hasOwnProperty;
+
+// The hoist function takes a FunctionExpression or FunctionDeclaration
+// and replaces any Declaration nodes in its body with assignments, then
+// returns a VariableDeclaration containing just the names of the removed
+// declarations.
+exports.hoist = function(funPath) {
+  t.assertFunction(funPath.node);
+
+  let vars = {};
+
+  function varDeclToExpr(vdec, includeIdentifiers) {
+    t.assertVariableDeclaration(vdec);
+    // TODO assert.equal(vdec.kind, "var");
+    let exprs = [];
+
+    vdec.declarations.forEach(function(dec) {
+      // Note: We duplicate 'dec.id' here to ensure that the variable declaration IDs don't
+      // have the same 'loc' value, since that can make sourcemaps and retainLines behave poorly.
+      vars[dec.id.name] = t.identifier(dec.id.name);
+
+      if (dec.init) {
+        exprs.push(t.assignmentExpression(
+          "=", dec.id, dec.init
+        ));
+      } else if (includeIdentifiers) {
+        exprs.push(dec.id);
+      }
+    });
+
+    if (exprs.length === 0)
+      return null;
+
+    if (exprs.length === 1)
+      return exprs[0];
+
+    return t.sequenceExpression(exprs);
+  }
+
+  funPath.get("body").traverse({
+    VariableDeclaration: {
+      exit: function(path) {
+        let expr = varDeclToExpr(path.node, false);
+        if (expr === null) {
+          path.remove();
+        } else {
+          // We don't need to traverse this expression any further because
+          // there can't be any new declarations inside an expression.
+          util.replaceWithOrRemove(path, t.expressionStatement(expr));
+        }
+
+        // Since the original node has been either removed or replaced,
+        // avoid traversing it any further.
+        path.skip();
+      }
+    },
+
+    ForStatement: function(path) {
+      let init = path.node.init;
+      if (t.isVariableDeclaration(init)) {
+        util.replaceWithOrRemove(path.get("init"), varDeclToExpr(init, false));
+      }
+    },
+
+    ForXStatement: function(path) {
+      let left = path.get("left");
+      if (left.isVariableDeclaration()) {
+        util.replaceWithOrRemove(left, varDeclToExpr(left.node, true));
+      }
+    },
+
+    FunctionDeclaration: function(path) {
+      let node = path.node;
+      vars[node.id.name] = node.id;
+
+      let assignment = t.expressionStatement(
+        t.assignmentExpression(
+          "=",
+          node.id,
+          t.functionExpression(
+            node.id,
+            node.params,
+            node.body,
+            node.generator,
+            node.expression
+          )
+        )
+      );
+
+      if (path.parentPath.isBlockStatement()) {
+        // Insert the assignment form before the first statement in the
+        // enclosing block.
+        path.parentPath.unshiftContainer("body", assignment);
+
+        // Remove the function declaration now that we've inserted the
+        // equivalent assignment form at the beginning of the block.
+        path.remove();
+      } else {
+        // If the parent node is not a block statement, then we can just
+        // replace the declaration with the equivalent assignment form
+        // without worrying about hoisting it.
+        util.replaceWithOrRemove(path, assignment);
+      }
+
+      // Don't hoist variables out of inner functions.
+      path.skip();
+    },
+
+    FunctionExpression: function(path) {
+      // Don't descend into nested function expressions.
+      path.skip();
+    }
+  });
+
+  let paramNames = {};
+  funPath.get("params").forEach(function(paramPath) {
+    let param = paramPath.node;
+    if (t.isIdentifier(param)) {
+      paramNames[param.name] = param;
+    } else {
+      // Variables declared by destructuring parameter patterns will be
+      // harmlessly re-declared.
+    }
+  });
+
+  let declarations = [];
+
+  Object.keys(vars).forEach(function(name) {
+    if (!hasOwn.call(paramNames, name)) {
+      declarations.push(t.variableDeclarator(vars[name], null));
+    }
+  });
+
+  if (declarations.length === 0) {
+    return null; // Be sure to handle this case!
+  }
+
+  return t.variableDeclaration("var", declarations);
+};