diff --git a/src/babel/api/browser.js b/src/babel/api/browser.js
index e9347934dc..715b0b471d 100644
--- a/src/babel/api/browser.js
+++ b/src/babel/api/browser.js
@@ -5,14 +5,14 @@ transform.version = require("../../../package").version;
 transform.transform = transform;
 
 transform.run = function (code, opts) {
-  opts = opts || {};
+  opts ||= {};
   opts.sourceMap = "inline";
   return new Function(transform(code, opts).code)();
 };
 
 transform.load = function (url, callback, opts, hold) {
-  opts = opts || {};
-  opts.filename = opts.filename || url;
+  opts ||= {};
+  opts.filename ||= url;
 
   var xhr = global.ActiveXObject ? new global.ActiveXObject("Microsoft.XMLHTTP") : new global.XMLHttpRequest();
   xhr.open("GET", url, true);
diff --git a/src/babel/api/node.js b/src/babel/api/node.js
index b367d697c4..b6edcb5bf3 100644
--- a/src/babel/api/node.js
+++ b/src/babel/api/node.js
@@ -50,7 +50,7 @@ exports.transformFile = function (filename, opts, callback) {
 };
 
 exports.transformFileSync = function (filename, opts) {
-  opts = opts || {};
+  opts ||= {};
   opts.filename = filename;
   return transform(fs.readFileSync(filename), opts);
 };
diff --git a/src/babel/api/register/node.js b/src/babel/api/register/node.js
index 334f757d62..b89c6544b9 100644
--- a/src/babel/api/register/node.js
+++ b/src/babel/api/register/node.js
@@ -136,7 +136,7 @@ hookExtensions(util.canCompile.EXTENSIONS);
 
 module.exports = function (opts) {
   // normalize options
-  opts = opts || {};
+  opts ||= {};
 
   if (opts.only != null) onlyRegex = util.regexify(opts.only);
   if (opts.ignore != null) ignoreRegex = util.regexify(opts.ignore);
diff --git a/src/babel/api/register/resolve-rc.js b/src/babel/api/register/resolve-rc.js
index 3a75faac86..dd6244f736 100644
--- a/src/babel/api/register/resolve-rc.js
+++ b/src/babel/api/register/resolve-rc.js
@@ -12,7 +12,7 @@ function exists(filename) {
 
 module.exports = function (loc, opts) {
   var rel = ".babelrc";
-  opts = opts || {};
+  opts ||= {};
 
   function find(start, rel) {
     var file = path.join(start, rel);
diff --git a/src/babel/generation/buffer.js b/src/babel/generation/buffer.js
index 385a8c5526..3b2a4522d4 100644
--- a/src/babel/generation/buffer.js
+++ b/src/babel/generation/buffer.js
@@ -78,7 +78,7 @@ Buffer.prototype.newline = function (i, removeLast) {
     return;
   }
 
-  removeLast = removeLast || false;
+  removeLast ||= false;
 
   if (isNumber(i)) {
     i = Math.min(2, i);
diff --git a/src/babel/generation/index.js b/src/babel/generation/index.js
index 016b051f1a..93babf3dbb 100644
--- a/src/babel/generation/index.js
+++ b/src/babel/generation/index.js
@@ -18,7 +18,7 @@ var n            = require("./node");
 var t            = require("../types");
 
 function CodeGenerator(ast, opts, code) {
-  opts = opts || {};
+  opts ||= {};
 
   this.comments = ast.comments || [];
   this.tokens   = ast.tokens || [];
@@ -108,7 +108,7 @@ CodeGenerator.prototype.buildPrint = function (parent) {
   };
 
   print.sequence = (nodes, opts) => {
-    opts = opts || {};
+    opts ||= {};
     opts.statement = true;
     return this.printJoin(print, nodes, opts);
   };
@@ -118,8 +118,8 @@ CodeGenerator.prototype.buildPrint = function (parent) {
   };
 
   print.list = function (items, opts) {
-    opts = opts || {};
-    opts.separator = opts.separator || ", ";
+    opts ||= {};
+    opts.separator ||= ", ";
     print.join(items, opts);
   };
 
@@ -146,7 +146,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
     this.format.concise = true;
   }
 
-  opts = opts || {};
+  opts ||= {};
 
   var newline = (leading) => {
     if (!opts.statement && !n.isUserWhitespacable(node, parent)) {
@@ -216,7 +216,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 CodeGenerator.prototype.printJoin = function (print, nodes, opts) {
   if (!nodes || !nodes.length) return;
 
-  opts = opts || {};
+  opts ||= {};
 
   var len = nodes.length;
 
diff --git a/src/babel/generation/node/whitespace.js b/src/babel/generation/node/whitespace.js
index dd3d66cb08..296ba55427 100644
--- a/src/babel/generation/node/whitespace.js
+++ b/src/babel/generation/node/whitespace.js
@@ -4,7 +4,7 @@ var map       = require("lodash/collection/map");
 var t         = require("../../types");
 
 var crawl = function (node, state) {
-  state = state || {};
+  state ||= {};
 
   if (t.isMemberExpression(node)) {
     crawl(node.object, state);
@@ -18,7 +18,7 @@ var crawl = function (node, state) {
   } else if (t.isFunction(node)) {
     state.hasFunction = true;
   } else if (t.isIdentifier(node)) {
-    state.hasHelper = state.hasHelper || isHelper(node.callee);
+    state.hasHelper ||= isHelper(node.callee);
   }
 
   return state;
diff --git a/src/babel/transformation/file.js b/src/babel/transformation/file.js
index 94187c6f33..a2c11bfe31 100644
--- a/src/babel/transformation/file.js
+++ b/src/babel/transformation/file.js
@@ -286,7 +286,7 @@ File.prototype.get = function (key) {
 };
 
 File.prototype.addImport = function (source, name, noDefault) {
-  name = name || source;
+  name ||= source;
   var id = this.dynamicImportIds[name];
 
   if (!id) {
@@ -312,7 +312,7 @@ File.prototype.isConsequenceExpressionStatement = function (node) {
 File.prototype.attachAuxiliaryComment = function (node) {
   var comment = this.opts.auxiliaryComment;
   if (comment) {
-    node.leadingComments = node.leadingComments || [];
+    node.leadingComments ||= [];
     node.leadingComments.push({
       type: "Line",
       value: " " + comment
@@ -353,7 +353,7 @@ File.prototype.logDeopt = function () {
 };
 
 File.prototype.errorWithNode = function (node, msg, Error) {
-  Error = Error || SyntaxError;
+  Error ||= SyntaxError;
 
   var loc = node.loc.start;
   var err = new Error("Line " + loc.line + ": " + msg);
@@ -429,7 +429,7 @@ var checkNode = function (stack, node, scope) {
 
 File.prototype.checkNode = function (node, scope) {
   var stack = this.transformerStack;
-  scope = scope || this.scope;
+  scope ||= this.scope;
 
   checkNode(stack, node, scope);
 
diff --git a/src/babel/transformation/index.js b/src/babel/transformation/index.js
index e5c53f335e..d0af8f05ce 100644
--- a/src/babel/transformation/index.js
+++ b/src/babel/transformation/index.js
@@ -58,7 +58,7 @@ var rawTransformers = require("./transformers");
 each(rawTransformers, function (transformer, key) {
   var namespace = key.split(".")[0];
 
-  transform.namespaces[namespace] = transform.namespaces[namespace] || [];
+  transform.namespaces[namespace] ||= [];
   transform.namespaces[namespace].push(key);
   transform.transformerNamespaces[key] = namespace;
 
diff --git a/src/babel/transformation/modules/_default.js b/src/babel/transformation/modules/_default.js
index 16abf3b269..3c64c498f2 100644
--- a/src/babel/transformation/modules/_default.js
+++ b/src/babel/transformation/modules/_default.js
@@ -33,7 +33,7 @@ DefaultFormatter.prototype.doDefaultExportInterop = function (node) {
 DefaultFormatter.prototype.bumpImportOccurences = function (node) {
   var source = node.source.value;
   var occurs = this.localImportOccurences;
-  occurs[source] = occurs[source] || 0;
+  occurs[source] ||= 0;
   occurs[source] += node.specifiers.length;
 };
 
diff --git a/src/babel/transformation/transformer.js b/src/babel/transformation/transformer.js
index aed6f765d2..d06c0f74eb 100644
--- a/src/babel/transformation/transformer.js
+++ b/src/babel/transformation/transformer.js
@@ -33,7 +33,7 @@ function Transformer(key, transformer, opts) {
   this.optional     = !!take("optional");
 
   this.handlers = this.normalize(transformer);
-  this.opts     = opts || {};
+  this.opts     ||= {};
   this.key      = key;
 }
 
diff --git a/src/babel/transformation/transformers/es6/block-scoping.js b/src/babel/transformation/transformers/es6/block-scoping.js
index bcabfcbb86..465f53f562 100644
--- a/src/babel/transformation/transformers/es6/block-scoping.js
+++ b/src/babel/transformation/transformers/es6/block-scoping.js
@@ -18,7 +18,7 @@ var isLet = function (node, parent) {
   if (isLetInitable(node, parent)) {
     for (var i = 0; i < node.declarations.length; i++) {
       var declar = node.declarations[i];
-      declar.init = declar.init || t.identifier("undefined");
+      declar.init ||= t.identifier("undefined");
     }
   }
 
diff --git a/src/babel/transformation/transformers/es6/classes.js b/src/babel/transformation/transformers/es6/classes.js
index 2623fdb377..6c13608a56 100644
--- a/src/babel/transformation/transformers/es6/classes.js
+++ b/src/babel/transformation/transformers/es6/classes.js
@@ -201,7 +201,7 @@ ClassTransformer.prototype.buildBody = function () {
   }
 
   if (instanceProps || staticProps) {
-    staticProps = staticProps || t.literal(null);
+    staticProps ||= t.literal(null);
 
     var args = [className, staticProps];
     if (instanceProps) args.push(instanceProps);
diff --git a/src/babel/transformation/transformers/es6/destructuring.js b/src/babel/transformation/transformers/es6/destructuring.js
index 87db9676eb..2743349afb 100644
--- a/src/babel/transformation/transformers/es6/destructuring.js
+++ b/src/babel/transformation/transformers/es6/destructuring.js
@@ -467,7 +467,7 @@ exports.VariableDeclaration = function (node, parent, scope, file) {
 
     for (i = 0; i < nodes.length; i++) {
       node = nodes[i];
-      declar = declar || t.variableDeclaration(node.kind, []);
+      declar ||= t.variableDeclaration(node.kind, []);
 
       if (!t.isVariableDeclaration(node) && declar.kind !== node.kind) {
         throw file.errorWithNode(node, messages.get("invalidParentForThisNode"));
diff --git a/src/babel/transformation/transformers/es6/tail-call.js b/src/babel/transformation/transformers/es6/tail-call.js
index 87ab030251..e2ff372e1e 100644
--- a/src/babel/transformation/transformers/es6/tail-call.js
+++ b/src/babel/transformation/transformers/es6/tail-call.js
@@ -23,23 +23,23 @@ function TailCallTransformer(node, scope, file) {
 }
 
 TailCallTransformer.prototype.getArgumentsId = function () {
-  return this.argumentsId = this.argumentsId || this.scope.generateUidIdentifier("arguments");
+  return this.argumentsId ||= this.scope.generateUidIdentifier("arguments");
 };
 
 TailCallTransformer.prototype.getThisId = function () {
-  return this.thisId = this.thisId || this.scope.generateUidIdentifier("this");
+  return this.thisId ||= this.scope.generateUidIdentifier("this");
 };
 
 TailCallTransformer.prototype.getLeftId = function () {
-  return this.leftId = this.leftId || this.scope.generateUidIdentifier("left");
+  return this.leftId ||= this.scope.generateUidIdentifier("left");
 };
 
 TailCallTransformer.prototype.getFunctionId = function () {
-  return this.functionId = this.functionId || this.scope.generateUidIdentifier("function");
+  return this.functionId ||= this.scope.generateUidIdentifier("function");
 };
 
 TailCallTransformer.prototype.getAgainId = function () {
-  return this.againId = this.againId || this.scope.generateUidIdentifier("again");
+  return this.againId ||= this.scope.generateUidIdentifier("again");
 };
 
 TailCallTransformer.prototype.getParams = function () {
diff --git a/src/babel/transformation/transformers/internal/alias-functions.js b/src/babel/transformation/transformers/internal/alias-functions.js
index 97332d9de8..77f299b7ee 100644
--- a/src/babel/transformation/transformers/internal/alias-functions.js
+++ b/src/babel/transformation/transformers/internal/alias-functions.js
@@ -46,10 +46,10 @@ var go = function (getBody, node, scope) {
 
   var state = {
     getArgumentsId() {
-      return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
+      return argumentsId ||= scope.generateUidIdentifier("arguments");
     },
     getThisId() {
-      return thisId = thisId || scope.generateUidIdentifier("this");
+      return thisId ||= scope.generateUidIdentifier("this");
     }
   };
 
@@ -60,7 +60,7 @@ var go = function (getBody, node, scope) {
   var body;
 
   var pushDeclaration = function (id, init) {
-    body = body || getBody();
+    body ||= getBody();
     body.unshift(t.variableDeclaration("var", [
       t.variableDeclarator(id, init)
     ]));
diff --git a/src/babel/transformation/transformers/internal/declarations.js b/src/babel/transformation/transformers/internal/declarations.js
index 2237a1ec6f..28119ab9f7 100644
--- a/src/babel/transformation/transformers/internal/declarations.js
+++ b/src/babel/transformation/transformers/internal/declarations.js
@@ -20,7 +20,7 @@ exports.Program = function (node, parent, scope, file) {
       if (declar.init) {
         node.body.unshift(file.attachAuxiliaryComment(t.variableDeclaration(kind, [declarNode])));
       } else {
-        kinds[kind] = kinds[kind] || [];
+        kinds[kind] ||= [];
         kinds[kind].push(declarNode);
       }
     }
diff --git a/src/babel/traversal/scope.js b/src/babel/traversal/scope.js
index cfa8475ccc..4d5f3d2dbc 100644
--- a/src/babel/traversal/scope.js
+++ b/src/babel/traversal/scope.js
@@ -170,7 +170,7 @@ Scope.prototype.checkBlockScopedCollisions = function (kind, name, id) {
 };
 
 Scope.prototype.rename = function (oldName, newName) {
-  newName = newName || this.generateUidIdentifier(oldName).name;
+  newName ||= this.generateUidIdentifier(oldName).name;
 
   var info = this.getBindingInfo(oldName);
   if (!info) return;
@@ -530,7 +530,7 @@ Scope.prototype.push = function (opts) {
   }
 
   if (t.isBlockStatement(block) || t.isProgram(block)) {
-    block._declarations = block._declarations || {};
+    block._declarations ||= {};
     block._declarations[opts.key] = {
       kind: opts.kind,
       id: opts.id,
diff --git a/src/babel/types/index.js b/src/babel/types/index.js
index 6dedf39288..c75a1d0e7b 100644
--- a/src/babel/types/index.js
+++ b/src/babel/types/index.js
@@ -22,7 +22,7 @@ function registerType(type, skipAliasCheck) {
   };
 
   t["assert" + type] = function (node, opts) {
-    opts = opts || {};
+    opts ||= {};
     if (!is(node, opts)) {
       throw new Error("Expected type " + JSON.stringify(type) + " with option " + JSON.stringify(opts));
     }
@@ -405,7 +405,7 @@ t.toIdentifier = function (name) {
  */
 
 t.ensureBlock = function (node, key) {
-  key = key || "body";
+  key ||= "body";
   return node[key] = t.toBlock(node[key], node);
 };