ES6 Support: do review comments left on proposed ES6 style guide

docs/es6_chromium.md

-<!-- This is feature markdown template
+<!-- Feature template markdown:
 ## Header
 
 **Usage Example:**
 
-``` js
+```js
 
 ```
 
 **Documentation:** [link]()
 
 **Discussion Notes / Link to Thread:**
 
 hyphen-hyphen-hyphen (change to actual hyphen)
-
 -->
 
-
 <style type="text/css">
   .doc {
     font-size: 16px;
   }
 
   .doc h2[id] {
     line-height: 20px;
     font-size: 16px;
   }
 
@@ skipping 21 matching lines @@
     display: none;
     padding: 0px 10px;
   }
 
   .feature-container.open > *:not(h2){
     display: block;
   }
 </style>
 
 <script>
-document.addEventListener("DOMContentLoaded", function(event) {
+document.addEventListener('DOMContentLoaded', function(event) {
   // Move all headers and corresponding contents to an accordion container.
-  document.querySelectorAll('h2[id]').forEach(function(header){
+  document.querySelectorAll('h2[id]').forEach(function(header) {
     var container = document.createElement('div');
     container.classList.add('feature-container');
     header.parentNode.insertBefore(container, header);
 
     // Add all the following siblings until it hits an <hr>

[dpapad, 2016/12/06 17:16:51]

Nit: Period missing at the end of the comment.

[Dan Beam, 2016/12/06 21:04:20]

Done.

-    var ele = header;
-    while(ele && ele.tagName !== 'HR') {
-      var nextEle = ele.nextElementSibling;
-      container.append(ele);
-      ele = nextEle;
+    var el = header;
+    while (el && el.tagName !== 'HR') {
+      var nextEl = el.nextElementSibling;
+      container.append(el);
+      el = nextEl;
     }
 
     // Add handler to open accordion on click.
-    header.addEventListener('click', () => {
+    header.addEventListener('click', function() {
       header.parentNode.classList.toggle('open');
     });
   });
 
   // Then remove all <hr>s since everything's accordionized.
-  document.querySelectorAll('hr').forEach(function(ele){
-    ele.parentNode.removeChild(ele);
+  document.querySelectorAll('hr').forEach(function(el) {

[dpapad, 2016/12/06 17:16:52]

Nit (optional): Can we use ES6 for this code?

document.querySelectorAll('hr').forEach((el) => el.parentNode.removeChild(el));

[Dan Beam, 2016/12/06 21:04:20]

not until we've allowed it, no (see above where I reverted an => to function()
{)

+    el.parentNode.removeChild(el);
   });
 });
 </script>
 
 [TOC]
 
 # ES6 Support In Chromium
 
 This is a list of new/updated features in ES6 specs that is being considered to
 be supported for Chromium development.
 
->**TBD:** Do we want to differenciate allow/ban status between subprojects? If
-so, how to denote?
+> **TBD:** Do we want to differenciate allow/ban status between subprojects? If
+> so, how to denote?
 
->**TBD:** Cross platform-build support?
+> **TBD:** Cross platform-build support?
 
 You can propose changing the status of a feature by sending an email to
 chromium-dev@chromium.org. Include a short blurb on what the feature is and why
 you think it should or should not be allowed, along with links to any relevant
 previous discussion. If the list arrives at some consensus, send a codereview
 to change this file accordingly, linking to your discussion thread.
 
->Some descriptions and Usage examples are from [kangax](https://kangax.github.

[Dan Beam, 2016/12/06 05:01:35]

btw, scottchen@, you can't break mid-word like this.  it breaks the formatting. 
i understand how this is at odd with our 80 col wrapping rule :(

-io/compat-table/es6/) and [http://es6-features.org/](http://es6-features.org/)
+> Some descriptions and Usage examples are from [kangax](https://kangax.github.io/compat-table/es6/)
+and [http://es6-features.org/](http://es6-features.org/)
 
 # Allowed Features
 
 The following features are allowed in Chromium development.
 
 ## `Promise`
 
-Built-in representation of a value that might be determined asynchronously,
-relieving developers from "callback hell".
+The Promise object is used for asynchronous computations. A Promise represents a
+value which may be available now, or in the future, or never.
 
 **Usage Example:**
 
-``` js
-function promiseA() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 100));
-}
+```js
+/** @type {!Promise} */
+var fullyLoaded = new Promise(function(resolve) {
+  function isLoaded() { return document.readyState == 'complete'; }
 
-function promiseB() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 200));
-}
+  if (isLoaded()) {
+    resolve();
+  } else {
+    document.onreadystatechange = function() {
+      if (isLoaded()) resolve();
+    };
+  }
+});
 
-function promiseC() {
-  return new Promise((resolve, reject) => setTimeout(resolve, 300));
-}
-
-Promise.all([promiseA(), promiseB(), promiseC()]).then(([a, b, c]) => {
-  someFunction(a, b, c);
-});
+// ... some time later ...
+loaded.then(startTheApp).then(maybeShowFirstRun);
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-promise-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-promise-objects)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)
 
 **Discussion Notes:** Feature already extensively used prior to creation of
 this document.
 
 ---
 
 # Banned Features
 
 The following features are banned for Chromium development.
 
 # Features To Be Discussed
 
 The following features are currently disallowed. See the top of this page on
 how to propose moving a feature from this list into the allowed or banned
 sections.
 
 ## `let` (Block-Scoped Variables)
 
-Declare variable that exists within the block scope. `let` can generally be
-used to replace `var` but `let` in global scope, unlike `var`, does not
-introduce a property on the global object.
+`let` declares a variable within the scope of a block.  This differs from `var`,
+which uses function level scope.
 
 **Usage Example:**
 
-``` js
-// This will make all buttons output "3".
-for(var i = 0; i < 3; i++) {
-  buttons[i].onclick = function() {
-    console.log(i);
-  };
+```js
+function varTest() {
+  var x = 1;
+  if (true) {
+    var x = 2;  // same variable!
+    console.log(x);  // 2
+  }
+  console.log(x);  // 2

[dpapad, 2016/12/06 17:16:51]

To make the two examples equivalent, the following line is missing.
var x = 'foo'; // No error

I still think that separating the runtime error to a separate example would be
more clear.

function f() {
  var a = 'hello';
  var a = 'hola'; // No error!

  let b = 'world';
  let b = 'mundo; // TypeError Identifier 'x' has already been declared.
}

[Dan Beam, 2016/12/06 21:04:20]

Done.

 }
 
-// This will make buttons output corresponding "i" values.
-for(let i = 0; i < 3; i++) {
-  buttons[i].onclick = function() {
-    console.log(i);
-  };
+function letTest() {
+  let x = 1;
+  if (true) {
+    let x = 2;  // different variable
+    console.log(x);  // 2
+                let x = 5;  // TypeError Identifier 'x' has already been declared.
+  }
+  console.log(x);  // 1
 }
-
-var bar = 1;
-var bar = 1; // No error thrown.
-
-let foo = 1;
-let foo = 1; // TypeError: Identifier 'foo' has already been declared.
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-let-and-const-declarations)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `const` (Block-Scoped Constants)
 
 Constants (also known as "immutable variables") are variables which cannot be
 re-assigned new content. Note that if the value is an object, the object itself
 is still mutable.
 
-`const` has traditionally been supported as a "function scoped" declaration
-like `var` (except in Internet Explorer), however in VMs supporting ES6 `const`
-is now a block scope declaration.
+Also note that in Chrome, `const` is block scoped like `let`.
 
 **Usage Example:**
 
-``` js
+```js
 const gravity = 9.81;
 gravity = 0; // TypeError: Assignment to constant variable.
+gravity === 9.81; // true
 
-gravity === 9.81; // true
+const frobber = {isFrobbing: true};
+frobber = {isFrobbing: false};  // TypeError: Assignment to constant variable.
+frobber.isFrobbing = false;  // works
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-let-and-const-declarations)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-let-and-const-declarations)
+
+**See also:** [Object.freeze()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `=>` (Arrow Functions)
 
 Arrow functions provide a concise syntax to create a function, and fix a number
 of difficulties with this (e.g. eliminating the need to write `const self =
 this`. Particularly useful for nested functions or callbacks.
 
-Prefer arrow functions over the function keyword, over `f.bind(this)`, and
-especially over `goog.bind(f, this)`.
+Prefer arrow functions over the function keyword and over `f.bind(this)`.
 
 Arrow functions has an implicit return when used without a body block.
 
 **Usage Example:**
 
-``` js
+```js
 // General usage, eliminating need for .bind(this).
 setTimeout(() => {
   this.doSomething();
 }, 1000);  // no need for .bind(this) or const self = this.
 
 // Another example...
 window.addEventListener('scroll', (event) => {
   this.doSomething(event);
 });  // no need for .bind(this) or const self = this.
 
 // Implicit return: returns the value if expression not inside a body block.
-() => 1 // returns 1
-() => {1} // returns undefined - body block does not implicitly return.
-() => {return 1;} // returns 1
+() => 1  // returns 1
+() => {1}  // returns undefined - body block does not implicitly return.
+() => {return 1;}  // returns 1
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-arrow-function-definitions)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-arrow-function-definitions)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Classes
 
-OOP-style and boilerplate-free class syntax, including inheritance, super(),
+OOP-style and boilerplate-free class syntax, including inheritance, `super()`,
 static members, and getters and setters.
 
 **Usage Example:**
 
-``` js
+```js
+// Note: let Shape = class {...}; also works

[dpapad, 2016/12/06 17:16:51]

This comment is probably more meaningful if placed after line 266.

[Dan Beam, 2016/12/06 21:04:20]

Done.

+
+class Shape {
+  constructor(x, y) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
 class Rectangle extends Shape {
-  constructor(id, x, y, width, height) {
+  constructor(x, y, width, height) {
     super(id, x, y);
     this.width  = width;
     this.height = height;
   }

[dpapad, 2016/12/06 17:16:52]

Nit: New line between functions?

[Dan Beam, 2016/12/06 21:04:20]

Done.

-  static defaultRectangle() {
-    return new Rectangle('default', 0, 0, 100, 100);
+  static goldenRectangle() {
+                var PHI = (1 + Math.sqrt(5)) / 2;

[dpapad, 2016/12/06 17:16:52]

Can we use "let" in all ES6 examples? Or at least all ES6 examples appearing
after the "let" example?

[Dan Beam, 2016/12/06 21:04:20]

i'm trying to use only 1 new concept at a time

+    return new Rectangle(0, 0, PHI, 1);
   }
-  move(x, y) {
-    this.x = x;
-    this.y = y;
-  }
-};
+}
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-class-definitions)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-class-definitions)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Block Scope Functions
 
 **Usage Example:**
 
-``` js
+```js
 {
   function foo() {
     return 1;
   }
   // foo() === 1
   {
     function foo() {
       return 2;
     }
     // foo() === 2
   }
   // foo() === 1
 }
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-functiondeclarationinstantiation)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-functiondeclarationinstantiation)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Default Function Parameters
 
+Initialize parameters with default values if no value or `undefined` is passed.
+
 **Usage Example:**
 
-``` js
-function f(x, y = 7, z = 42) {
-  return x + y + z;
+```js
+/**
+ * @param {!Element} element An element to hide.
+ * @param {boolean=} animate Whether to animatedly hide |element|.
+ */
+function hide(element, animate=true) {
+  function setHidden() { element.hidden = true; }
+
+  if (animate)
+    element.animate({...}).then(setHidden);
+  else
+    setHidden();
 }
-// f(1) === 50;
+
+hide(document.body);  // animated, animate=true by default
+hide(document.body, false);  // not animated
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-functiondeclarationinstantiation)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-functiondeclarationinstantiation)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Rest Parameters
 
 Aggregation of function arguments into one Array variable.
 
 **Usage Example:**
 
-``` js
-function f(x, y, ...a) {
-  // for f(1, 2, 3, 4, 5)...
-    // x = 1, y = 2
-    // a = [3, 4, 5]
+```js
+function usesRestParams(a, b, ...theRest) {
+  console.log(a);  // 'a'
+  console.log(b);  // 'b'
+  console.log(theRest);  // [1, 2, 3]
 }
+
+usesRestParams('a', 'b', 1, 2, 3);
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-function-definitions)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-function-definitions)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Spread Operators
 
 Spreading the elements from an iterable collection into individual literals as
 function parameters.
 
 **Usage Example:**
 
-``` js
+```js
 // Spreading an Array
-var params = [ 'hello', true, 7 ];
-var other = [ 1, 2, ...params ]; // [ 1, 2, 'hello', true, 7 ]
-f(1, 2, ...params) === 9;
+var params = ['hello', true, 7];
+var other = [1, 2, ...params]; // [1, 2, 'hello', true, 7]
 
 // Spreading a String
 var str = 'foo';
-var chars = [ ...str ]; // [ 'f', 'o', 'o' ]
+var chars = [...str]; // ['f', 'o', 'o']
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-argument-lists-runtime-semantics-argumentlistevaluation)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-argument-lists-runtime-semantics-argumentlistevaluation)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Object Literal Extensions
 
 Convenient new ways for object property definition.
 
 **Usage Example:**
 
-``` js
+```js
 // Computed property name
-var x = 'key';
-var obj = {[x]: 1};
+var prop = 'foo';
+var o = {
+  [prop]: 'hey',
+  ['b' + 'ar']: 'there',
+};
+console.log(o);  // {foo: 'hey', bar: 'there'}
 
 // Shorthand property
-var obj = {x, y}; //equivalent to {x:x, y:y}
+var foo = 1;
+var bar = 2;
+var o = {foo, bar};
+console.log(o);  // {foo: 1, bar: 2}
 
 // Method property
-var obj = {
-  foo() {...},
-  bar() {...}
-}
+var clearSky = {
+  // basically the same as clouds: function() { return 0; }
+  clouds() { return 0; },
+  color() { return 'blue'; },
+};
+console.log(clearSky.color());  // 'blue'
+console.log(clearSky.clouds());  // 0
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-object-initialiser)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-object-initialiser)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Template Literals
 
 Expression interpolation for Strings, with the ability to access raw template
 pieces.
 
 **Usage Example:**
 
-``` js
+```js
 // Simple example
 var greeting = 'hello';
 var myName = {first: 'Foo', last: 'Bar'};
 var message = `${greeting},
 my name is ${myName.first + myName.last}`;
 // message == 'hello,\nmy name is FooBar'
-
-// Custom interpolation
-function foo (strings, ...values) {
-  // for foo`bar${42}baz`...
-    // strings[0] === 'bar';
-    // strings[1] === 'baz';
-    // values[0] === 42;
-
-  return strings[1] + strings[0] + values[0];
-}
-
-var newString = foo`bar${42}baz`; // 'bazbar42'
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-template-literals)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-template-literals)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Binary & Octal Literals
 
 **Usage Example:**
 
-``` js
+```js
 0b111110111 === 503;
 0o767 === 503;
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-literals-numeric-literals)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-literals-numeric-literals)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `/u` Unicode Regex Literal
 
 **Usage Example:**
 
-``` js
+```js
 '𠮷'.match(/./u)[0].length === 2;
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-get-regexp.prototype.sticky)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-get-regexp.prototype.sticky)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `\u{}` Unicode String
 
 **Usage Example:**
 
-``` js
+```js
 '\u{1d306}' == '\ud834\udf06'; // true
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-literals-string-literals)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-literals-string-literals)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `/y` Regex Sticky Matching
 
 Keep the matching position sticky between matches and this way support
-efficient parsing of arbitrary long input strings, even with an arbitrary
+efficient parsing of arbitrarily long input strings, even with an arbitrary
 number of distinct regular expressions.
 
 **Usage Example:**
 
-``` js
+```js
 var re = new RegExp('yy', 'y');
 re.lastIndex = 3;
 var result = re.exec('xxxyyxx')[0];
 result === 'yy' && re.lastIndex === 5; // true
 ```
 
-**Documentation:** [link](http://es6-features.org
-/#RegularExpressionStickyMatching)
+**Documentation:** [link](http://es6-features.org/#RegularExpressionStickyMatching)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Destructuring Assignment
 
 Flexible destructuring of collections or parameters.
 
 **Usage Example:**
 
-``` js
+```js
 // Array
-var list = [ 1, 2, 3 ];
-var [ a, , b ] = list;
-// a = 1, b = 3
+var [a, , b] = [1, 2, 3];  // a = 1, b = 3
 
 // Object
-var {width, height, area: a} = rect;
-// width = rect.width, height = rect.height, a = rect.area
+var {width, height} = document.body.getBoundingClientRect();
+// width = rect.width, height = rect.height
 
 // Parameters
-function f ([ name, val ]) {
-  console.log(name, val);
+function f([name, val]) {
+  console.log(name, val);  // 'bar', 42
 }
-function g ({ name: n, val: v }) {
-  console.log(n, v);
+f(['bar', 42]);

[dpapad, 2016/12/06 17:16:52]

What happens if user calls it as follows? Can we add this to the example?
f([1, 2, 3, 4]);

Assuming extra array members are ignored?
f([1, 2, 3, 4]); // 1, 2

[Dan Beam, 2016/12/06 21:04:20]

Done.

+
+function g({name: n, val: v}) {
+  console.log(n, v);  // 'foo', 7
 }
-function h ({ name, val }) {
-  console.log(name, val);
+g({name: 'foo', val:  7});
+
+function h({name, val}) {
+  console.log(name, val);  // 'bar', 42
 }
-
-f([ 'bar', 42 ]);
-g({ name: 'foo', val:  7 });
-h({ name: 'bar', val: 42 });
+h({name: 'bar', val: 42});
 
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-destructuring-assignment)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-destructuring-assignment)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Modules
 
 Support for exporting/importing values from/to modules without global
 namespace pollution.
 
 **Usage Example:**
 
-``` js
+```js
 // lib/rect.js
 export function getArea() {...};
-export { width, height, unimportant };
+export {width, height, unimportant};
 
 // app.js
 import {getArea, width, height} from 'lib/rect';
 
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-modules)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-modules)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Symbol Type
 
 Unique and immutable data type to be used as an identifier for object
 properties.
 
 **Usage Example:**
 
-``` js
+```js
 const foo = Symbol();
 const bar = Symbol();
 typeof foo === 'symbol'; // true
 typeof bar === 'symbol'; // true
 let obj = {};
 obj[foo] = 'foo';
 obj[bar] = 'bar';
 JSON.stringify(obj); // {}
 Object.keys(obj); // []
 Object.getOwnPropertyNames(obj); // []
-Object.getOwnPropertySymbols(obj); // [ foo, bar ]
+Object.getOwnPropertySymbols(obj); // [foo, bar]
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-symbol-constructor)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-symbol-constructor)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `for ...of` Loops
 
-Convenient operator to iterate over all values of an iterable object.
+Convenient operator to iterate over all values in an iterable collection. This
+differs from `for ...in`, which iterates over all iterable properties.
 
 **Usage Example:**
 
-``` js
-// Given an iterable  collection `fibonacci`...
-for (let n of fibonacci) {
-  console.log(n);
+```js
+// Given an iterable collection fibonacci numbers...
+for (var n of fibonacci) {
+  console.log(n);  // 1, 1, 2, 3, ...
 }
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-for-in-and-for-of-statements)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-for-in-and-for-of-statements)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Object Static Methods
 
 **Usage Example:**
 
-``` js
+```js
 // Object.assign
 var o = Object.assign({a:true}, {b:true}, {c:true});
 'a' in o && 'b' in o && 'c' in o; // true
 
 // Object.setPrototypeOf
 Object.setPrototypeOf({}, Array.prototype) instanceof Array; //true
 
 // Object.is
 // Object.getOwnPropertySymbols
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-object-constructor)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-properties-of-the-object-constructor)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## String Static & Prototype methods
 
 **Usage Example:**
 
-``` js
+```js
 // String.raw
 // String.fromCodePoint
 
 // String.prototype.codePointAt
 // String.prototype.normalize
 // String.prototype.repeat
 // String.prototype.startsWith
 // String.prototype.endsWith
 // String.prototype.includes
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-string-constructor)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-properties-of-the-string-constructor)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Array Static & Prototype Methods
 
 **Usage Example:**
 
-``` js
+```js
 // Array.from
 // Array.of
 
 // Array.prototype.copyWithin
 // Array.prototype.find
 // Array.prototype.findIndex
 // Array.prototype.fill
 // Array.prototype.keys
 // Array.prototype.values
 // Array.prototype.entries
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-properties-of-the-array-constructor)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-properties-of-the-array-constructor)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Number Properties
 
 **Usage Example:**
 
-``` js
+```js
 // Number.isFinite
 // Number.isInteger
 // Number.isSafeInteger
 // Number.isNaN
 // Number.EPSILON
 // Number.MIN_SAFE_INTEGER
 // Number.MAX_SAFE_INTEGER
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-isfinite-number)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-isfinite-number)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Iterators
 
 **Usage Example:**
 
-``` js
+```js
 let fibonacci = {
   [Symbol.iterator]() {
     let pre = 0, cur = 1;
     return {
       next () {
-        [ pre, cur ] = [ cur, pre + cur ];
-        return { done: false, value: cur };
+        [pre, cur] = [cur, pre + cur];
+        return {done: false, value: cur};
       }
     };
   }
 };
 ```
 
 **Documentation:** [link]()
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Generators
 
 Special iterators with specified pausing points.
 
 **Usage Example:**
 
-``` js
+```js
 function* range(start, end, step) {
   while (start < end) {
     yield start;
     start += step;
   }
 }
 
 for (let i of range(0, 10, 2)) {
   console.log(i); // 0, 2, 4, 6, 8
 }
 
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-generator-function-definitions)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-generator-function-definitions)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `Map`
 
+A simple key/value map in which any value (both objects and primitive values)
+may be used as either a key or a value.
+
 **Usage Example:**
 
-``` js
+```js
+var map = new Map();
+map.size === 0; // true
+map.get('foo'); // undefined
+
 var key = {};
-var map = new Map();
+map.set(key, 123);
+map.size === 1; // true
+map.has(key); // true
+map.get(key); // 123
 
-map.set(key, 123);
-
-map.has(key) && map.get(key) === 123; // true
+map.delete(key);
+map.has(key); // false;
+map.size === 0; // true
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-map-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-map-objects)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `Set`
 
+An object that lets you store unique values of any type, whether primitive
+values or object references.
+
 **Usage Example:**
 
-``` js
-var obj = {};
+```js
 var set = new Set();
 
 set.add(123);
+set.size();  // 1
+set.has(123);  // true
+
 set.add(123);
-
-set.has(123); // true
+set.size();  // 1
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-set-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-set-objects)
+[link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `WeakMap`
 
 WeakMap does not prevent garbage collection if nothing else refers to an object
 within the collection.
 
 **Usage Example:**
 
-``` js
+```js
 var key = {};
 var weakmap = new WeakMap();
 
 weakmap.set(key, 123);
 
 weakmap.has(key) && weakmap.get(key) === 123; // true
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-weakmap-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-weakmap-objects)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `WeakSet`
 
 WeakSet does not prevent garbage collection if nothing else refers to an object
 within the collection.
 
 **Usage Example:**
 
-``` js
+```js
 var obj1 = {};
 var weakset = new WeakSet();
 
 weakset.add(obj1);
 weakset.add(obj1);
 
 weakset.has(obj1); // true
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-weakset-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-weakset-objects)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Typed Arrays
 
 A lot of new typed Arrays...
 
 **Usage Example:**
 
-``` js
+```js
 new Int8Array();
 new UInt8Array();
-new UInt8ClampedArray()
-// ...You get the idea. Click on the Documentation link below to see all.
+new UInt8ClampedArray();
+// ... You get the idea. Click on the Documentation link below to see all.
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-typedarray-objects)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-typedarray-objects)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `Proxy`
 
 Hooking into runtime-level object meta-operations.
 
 **Usage Example:**
 
-``` js
-let target = {
-  foo: 'Welcome, foo'
-};
-let proxy = new Proxy(target, {
-  get (receiver, name) {
-    return name in receiver ? receiver[name] : `Hello, ${name}`;
-  }
+```js
+var keyTracker = new Proxy({}, {
+  keysCreated: 0,
+
+  get (receiver, key) {
+    if (key in receiver) {
+      console.log('key already exists');
+    } else {
+      ++this.keysCreated;
+      console.log(this.keysCreated + ' keys created!');
+      receiver[key] = true;
+    }
+  },
 });
-proxy.foo === 'Welcome, foo'; // true
-proxy.world === 'Hello, world'; // true
+
+keyTracker.key1;  // 1 keys created!
+keyTracker.key1;  // key already exists
+keyTracker.key2;  // 2 keys created!
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-proxy-object-internal-methods-and-internal-slots)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-proxy-object-internal-methods-and-internal-slots)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## `Reflection`
 
 Make calls corresponding to the object meta-operations.
 
 **Usage Example:**
 
-``` js
-let obj = { a: 1 };
-Object.defineProperty(obj, 'b', { value: 2 });
+```js
+let obj = {a: 1};
+Object.defineProperty(obj, 'b', {value: 2});
 obj[Symbol('c')] = 3;
 Reflect.ownKeys(obj); // ['a', 'b', Symbol(c)]
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-reflection)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-reflection)
 
 **Discussion Notes / Link to Thread:**
 
 ---
 
 ## Math Methods
 
 A lot of new Math methods.
 
 **Usage Example:**
 
-``` js
+```js
 // See Doc
 ```
 
-**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0
-/#sec-math)
+**Documentation:** [link](http://www.ecma-international.org/ecma-262/6.0/#sec-math)
 
 **Discussion Notes / Link to Thread:**
 
 ---