Index. Symbols. accessor properties, 74,

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1 Index Symbols * (asterisk), , 157, 159, 175 ** (exponentiation operator), \ (backslash), 26 ` (backtick), 26 : (colon), 69, 88 {} (curly braces), 56 57, 88 89, 285 ${ } (substitution delimiters), (rest items), (rest parameters), (spread operator), converting sets to arrays, 126 nonarray iterables and, = (equal sign), 87 == (equals operator), 72 === (identically equals operator), 72 (logical OR operator), 36 [] (square brackets), A accessor properties, 74, add() method, for sets, for weak sets, apply() method, 47 48, 51, 61 apply trap, 245, , 268 arguments object arrow functions and, 55, 60 effect of default parameter values on, effect of rest parameters on, ArrayBuffer constructor, 200 array buffers, creating, manipulating with views, reading and writing data, retrieving view infor ma tion, 201 type-specific views, Array constructor, Array.from() method, mapping conversion, using on iterables, Array.isArray() method, 209 Array.of() method, Array.prototype.includes() method, arrays, arrow functions and, 60 converting sets to, 126 creating, Array.from() method, Array.of() method, creating objects that behave as, 244, deleting elements when reducing length, detecting array indexes, 270 implementing MyArray class, increasing length when adding new elements, destructuring for, default values, 92 destructuring assignment, mixed with object destructuring, nested array destructuring, 92 rest items, methods for, copywithin() method, fill() method, 197 findindex() method, find() method, typed, array buffers, element size, 206 numeric data types, 199 regular arrays versus, views, arrow functions, arguments binding, 60 arrays and, 60 compared to other functions, identifying, 61

2 arrow functions, continued immediately invoked function expressions, syntax for, this binding, assignments, destructuring arrays, objects, asterisk (*), , 157, 159, 175 asynchronous module loading, asynchronous programming, See also promises callbacks, events, asynchronous task running, , asynchronous task runner example, await syntax, 240 simple task runner example, task running with data, await syntax, 240 B backslash (\), 26 backtick (`), 26 Basic Multilingual Plane (BMP), 14, 16 bind() method, 49 block bindings, 1 12 declarations, 2 7 const declarations, 4 6 let declarations, 3 4 redeclaration, 4 temporal dead zone, 6 7 var declarations, 2 3 emerging best practices for, 12 global, hoisting, 2 3 in loops, 7 11 const declarations, functions, 8 let declarations, 9 10 block-level functions, in non-strict mode, 54 when to use, 53 block scopes (lexical scopes), 3 BMP (Basic Multilingual Plane), 14, 16 buffer property, 201, 205 built-in iterators, collection iterators, default for collection types, entries() iterator, 146 keys() iterator, values() iterator, NodeList iterators, 151 string iterators, built-in objects, 68 bytelength property, 201, 205 byteoffset property, 201, 205 BYTES_PER_ELEMENT property, 206 C callbacks, call() function, 61 [[Call]] method, canonical equivalence, 16 catch() method, , 221, 225, , charat() method, charcodeat() method, checkargs() method, 46 classes, accessor properties, class constructors callable, new.target in, overriding abstract, class declarations, basic, syntax for, class expressions, basic, named, class-like structures in ECMAScript 5, 166 computed member names, constant class names, 169 derived, from expressions, inherited static members, 181 inheriting from built-ins, shadowing class methods, Symbol.species property, as first-class citizens, generator methods, Index

3 static members, , 181 using proxies as prototypes on, class keyword, 166 clear() method for maps, 130 for sets, clone() method, codepointat() method, code points, code units, collection iterators, default for collection types, entries() iterator, 146 keys() iterator, values() iterator, colon (:), 69, 88 computed member names, computed property names, concat() method, 93, , concise method syntax, console.log() method, 61, 103 const declarations, 4 5 in global scope, 11 let declarations versus, 5 in loops, for objects, 6 temporal dead zone, 6 using by default, 11 [[Construct]] method, constructors, construct trap, 245, copywithin() method, , 207 CORS (Cross-Origin Resource Sharing), 296 count variable, 4 createiterator() function, create() method, 181 Crockford, Douglas, 113 Cross-Origin Resource Sharing (CORS), 296 curly braces ({}), 56 57, 88 89, 285 D DataView type, default keyword, default parameter values, default parameter expressions, for destructured parameters, in ECMAScript 5, 36 in ECMAScript 6, effect on arguments object, object destructuring, temporal dead zone, defineproperty trap, 245, delete() method for maps, 130 for sets, for weak maps, for weak sets, delete operator, 250 deleteproperty trap, 245, derived classes, from expressions, inherited static members, 181 inheriting from built-ins, shadowing class methods, Symbol.species property, destructuring, for arrays, default values, 92 destructuring assignment, nested array destructuring, 92 rest items, for-of loops and, 149 initializers and, 85 mixed, for objects, assigning to different local variable names, default values, destructuring assignment, nested object destructuring, for parameters, default values, required, usefulness of, 84 domain-specific languages (DSLs), 25 E ECMAScript 2016 (ECMAScript 7), 305 Array.prototype.includes() method, exponentiation operator, function-scoped strict mode, Index 313

4 endswith() method, entries() iterator, , 148, enumerate trap, 245 equal sign (=), 87 equals operator (==), 72 error-first callback style, 215 events, exec() method, 23 exotic objects, 68 exponentiation operator (**), exporting to modules, re-exporting bindings, renaming exports, export keyword, extends keyword, 178 F factorial() method, 64 failure() method, fill() method, , 207 filter() method, 207 findindex() method, , 207 find() method, , 207 first-class citizens, classes as, flags property, Float32Array constructor, 204 Float64Array constructor, 204 foreach() method, 207 for maps, for sets, for-in loops const declarations in, let declarations in, 9 10 own property enumeration order, 76 for loops, 7 9 const declarations in, 10 let declarations in, 9 10 var declarations in, 7 8 for-of loops const declarations in, destructuring and, 149 iterables and, accessing default iterator, creating iterables, let declarations in, 9 10 from() method, func() method, 63 Function constructor, functions, See also names of specific functions arrow, arguments binding, 60 arrays and, 60 compared to other functions, identifying, 61 immediately invoked function expressions, syntax for, this binding, block-level, in non-strict mode, 54 when to use, 53 constructors, with default parameter values, default parameter expressions, in ECMAScript 5, 36 in ECMAScript 6, effect on arguments object, temporal dead zone, Function constructor, in loops, 8 name property, spread operator, tail call optimization, in ECMAScript 6, making use of, unnamed parameters, in ECMAScript 5, rest parameters, G generators, , asynchronous task running, asynchronous task runner example, simple task runner example, task running with data, delegating, function expressions for, 141 loops and complexity, 138 methods for, object methods for, 142 return statements, getfloat32() method, Index

5 getfloat64() method, 202 getint8() method, getint16() method, 203 get() method for maps, 129 for weak maps, getownpropertydescriptor trap, 245, getprototypeof trap, 245, get trap, 245 object shape validation using, using on prototypes, getuint8() method, 202 getvalue() function, 2 3, g flag, 22, 24 global block bindings, H handlers, 245 has() method for maps, 130 for sets, 123 for weak maps, for weak sets, has trap, 245 hiding property existence using, using on prototypes, hoisting, 2 3, 53 [[HomeObject]] property, HTML escaping, 25 I identically equals operator (===), 72 i flag, 24 if statements, immediately invoked function expressions (IIFEs), 8 9, 57 58, 135, 168 importing modules, entire module, multiple bindings, 286 quirk of imported bindings, 288 renaming imports, single binding, 286 without bindings, 292 import keyword, 285 includes() method, 19 20, indentlevel variable, 21 indexof() method, 19 20, , 207 inheritance. See derived classes initializers, destructuring and, 85 init() method, in operator, 122 instanceof, 50 Int8Array constructor, Int16Array constructor, Int32Array constructor, 204, 206 integers, isextensible trap, 245, iterables, 142 creating typed arrays, 205 for-of loops and, accessing default iterator, creating iterables, spread operator and nonarray, using Array.from() method on, iterators, , , asynchronous task running, asynchronous task runner example, simple task runner example, task running with data, built-in, collection iterators, NodeList iterators, 151 string iterators, for-of loops and iterables, accessing default iterator, creating iterables, loops and complexity, 138 passing arguments to, spread operator and nonarray iterables, throwing errors in, i variable, 7 9 J job queues, 214 job scheduling, 220 join() method, 207 json2.js, 113 JSON global object, 113 JSON.stringify() method, 76 Index 315

6 K keys() iterator, 145, , L lastindexof() method, 19 20, , 207 let declarations const declarations versus, 5 in global scope, 11 in loops, 9 10 no redeclaration, 4 syntax for, 3 4 temporal dead zone, 6 lexical scopes (block scopes), 3 little-endian, 202 loading modules, asynchronous module loading, browser module specifier resolution, 297 loading sequence, <script> element, as workers, 296 localname variable, localtype variable, 87 logical OR operator ( ), 36 loops. See also names of specific loops block bindings in, 7 11 const declarations in loops, functions in loops, 8 let declarations in loops, 9 10 complexity and, 138 M makerequest() method, Map constructor, 131 map() method, maps, , array conversion with mapping functions, in ECMAScript 5, foreach() method for, initializing, 131 methods for, 130 rejection handling, weak, initializing, 133 limitations of, 136 methods for, private object data, using, match() method, 18, 109 Math.max() method, Math object methods, MAX_SAFE_INTEGER property, 300 memory leaks, 127 metaproperties, 51 methods. See also names of specific methods for arrays, copywithin() method, fill() method, 197 findindex() method, find() method, typed versus regular, formal definition, for generators, 142, for identifying substrings, for maps, 130 math, on Object global, accessor properties, 74 Object.assign() method, Object.is() method, 72 for weak maps, MIN_SAFE_INTEGER property, 300 mixargs() function, mixin() function, 73, 183 mixins, 72 modules, default values, exporting, importing, exporting, re-exporting bindings, renaming exports and imports, importing, entire module, multiple bindings, 286 quirk of imported bindings, 288 renaming imports, single binding, 286 without bindings, 292 loading, asynchronous module loading, browser module specifier resolution, 297 loading sequence, Index

7 <script> element, as workers, 296 syntax limitations, 287 module specifiers, 285, 297 multiline strings, N name property, 48 49, 55 choosing appropriate names, 48 concise method syntax, 70 special cases of, 49 nested array destructuring, 92 nested object destructuring, new.target metaproperty, 51 52, , next() method for iterators, , 143 passing arguments to iterators, return statements for generators, simple task runners, 160 task running with data, throwing errors in iterators, NodeList iterators, 151 normalization forms, normalize() method, Number.isInteger() method, Number.isSafeInteger() method, numeric data types, for typed arrays, 199 O Object.assign() method, 72 75, Object.create() method, 76, 116, 279 Object.defineProperties() method, Object.defineProperty() method, 101, 106, 167, 243, , 275 object extensibility traps, duplicate extensibility methods, examples of, Object.freeze() method, 248 Object.getOwnPropertyDescriptor() method, Object.getOwnPropertyNames() method, 75 76, 104, Object.getOwnPropertySymbols() method, 104, Object.getPrototypeOf() method, 76, 78 79, , object literals duplicate properties, 75 syntax extensions, computed property names, concise method syntax, property initializer shorthand, Object.isExtensible() method, Object.is() method, 72, 122 Object.keys() method, 76, 104, Object.preventExtensions() method, 248, Object.prototype.toString() method, objects, categories of, 68 destructuring for, assigning to different local variable names, default values, destructuring assignment, mixed with array destructuring, nested object destructuring, duplicate object literal properties, 75 method definition, methods on Object global, accessor properties, 74 Object.assign() method, Object.is() method, 72 object literal syntax extensions, computed property names, concise method syntax, property initializer shorthand, own property enumeration order, prototypes, accessing with super references, changing, Object.seal() method, 248 Object.setPrototypeOf() method, 76 77, 252, 254, Index 317

8 of() method, onclick event, ordinary objects, 68 outputinfo() function, 86 ownkeys trap, 245, own properties creating, 167 enumeration order, P parameters default values, default parameter expressions, destructured parameters, in ECMAScript 5, 36 in ECMAScript 6, effect on arguments object, object destructuring, temporal dead zone, destructured, default values, required, unnamed, in ECMAScript 5, rest parameters, validating, pick() method, 44 pop() method, 210 p parameter, 64 preventextensions trap, 245, Promise constructor, 219 Promise.reject() method, Promise.resolve() method, , promises, asynchronous task running, chaining, catching errors, returning promises in promise chains, returning values in promise chains, global rejection handling, browser rejection handling, Node.js rejection handling, inheriting from, life cycle of, responding to multiple, Promise.all() method, Promise.race() method, settled, executor errors, 224 unsettled, property descriptor traps, blocking Object.defineProperty(), defineproperty() methods, descriptor object restrictions, duplicate descriptor methods, 260 getownpropertydescriptor() methods, 261 property initializer shorthand syntax, proto property, prototype property, 54 [[Prototype]] property, 77 prototypes, accessing with super references, changing, prototype proxy traps, function of, purpose of two sets of methods, using proxies as, on classes, using get trap on prototypes, using has trap on prototypes, using set trap on prototypes, proxies, creating, 244, function proxies, callable class constructors, calling constructors without new, overriding abstract base class constructors, validating function parameters, hiding property existence, Index

9 mimicking array behavior, 244, deleting elements when reducing length, detecting array indexes, 270 implementing the MyArray class, increasing length when adding new elements, object extensibility traps, duplicate extensibility methods, examples of, object shape validation, ownkeys trap, preventing property deletion, property descriptor traps, blocking Object.defineProperty(), defineproperty() methods, descriptor object restrictions, duplicate descriptor methods, 260 getownpropertydescriptor() methods, 261 prototype proxy traps, function of, purpose of two sets of methods, revocable proxies, using as prototypes, on classes, using get trap on prototypes, using has trap on prototypes, using set trap on prototypes, validating properties, Proxy.revocable() method, push() method, 210 R readfile() function, , , 240 reduce() method, 207 reduceright() method, 207 Reflect.apply() method, 263 Reflect.construct() method, 263, Reflect.defineProperty() method, 257, Reflect.deleteProperty() method, 251 reflect() function, 56 Reflect.get() method, 248, 273 Reflect.getOwnPropertyDescriptor() method, 257, Reflect.getPrototypeOf() method, 252, 254 Reflect.has() method, reflection API, 244. See also proxies Reflect.isExtensible() method, Reflect object, 244 Reflect.ownKeys() method, Reflect.preventExtensions() method, Reflect.set() method, , 271, 278 Reflect.setPrototypeOf() method, 252, 254 RegExp variable, 11, 19, regular expressions duplicating, flags property, importance of, 13 u flag, y flag, rejectionhandled event, rejectionhandled event, reject() method, , 231 repeat() method, replace() method, 109 resolve() method, , 230 rest items (...), rest parameters (...), return statements, for generators, reverse() method, 207 revoke() function, 269 run() function, 160, S <script> element, scripts, 284 search() method, 109 Set constructor, setcookie() function, setfloat32() method, 202 Index 319

10 setfloat64() method, 202 setint8() method, setinterval() function, 220, 226 set keyword, 173 set() method, 132, 211 setprototypeof trap, 245, sets, , 136 adding items, converting to arrays, 126 creating, 122 in ECMAScript 5, foreach() method for, removing items, weak, creating, regular versus, settimeout() function, settled promises, 217, executor errors, 224 set trap, 245 using on prototypes, validating properties using, setuint8() method, 202 shift() method, 210 single-threaded event loops, 214 slice() method, 185, 194, 200, 207 some() method, 207 sort() method, 207 splice() method, 210 split() method, 109 spread operator (...), converting sets to arrays, 126 nonarray iterables and, square brackets ([]), standard objects, 68 startswith() method, static keyword, 177 static members, , 181 step() method, 160, sticky regular expressions, strict mode, changes to, String.fromCodePoint() method, 16 String() function, string iterators, String.raw() tag, strings, importance of, 13 methods for identifying substrings, repeat() method, template literals, making substitutions, multiline strings, syntax for, 26 tagged templates, Unicode support, codepointat() method, normalize() method, String.fromCodePoint() method, 16 UTF-16 code points, 14 15, 18 subarray() method, 211 substitutions, substrings, methods for identifying, success() method, sum() function, 56, 61, 264 super() method, 77 80, 179, 180, 183, 189 supplementary planes, 14 surrogate pairs, 14 Symbol.for() method, Symbol function, 100 Symbol.hasInstance() method, Symbol.isConcatSpreadable property, 105, Symbol.iterator() method, 105, , 176 Symbol.keyFor() method, 103 Symbol.match property, 105, Symbol.replace property, 105, symbols, coercion of, 103 creating, 100 exposing internal operations with, identifying, 101 retrieving properties of, sharing, using, Symbol.search property, 105, Symbol.species property, 105, Symbol.split property, 105, Symbol.toPrimitive() method, 105, Symbol.toStringTag property, 105, defining object string tags, identification problem workaround, 113 Symbol.unscopables property, 105, Index

11 T tagged templates, defining tags, using raw values in template literals, tail call optimization, in ECMAScript 6, making use of, targets, TDZ (temporal dead zone), 6 7, template literals, multiline strings, substitutions, syntax for, 26 tagged templates, defining tags, raw values, temporal dead zone (TDZ), 6 7, test() method, 23 then() method, , , 225, this binding, 54, throw() method, tostring() method, 100, 111, traps, function proxies with, callable class constructors, calling constructors without new, overriding abstract base class constructors, validating function parameters, hiding property existence using, object extensibility, duplicate extensibility methods, examples of, object shape validation using, ownkeys, preventing property deletion with, property descriptor, blocking Object.defineProperty(), defineproperty() methods, descriptor object restrictions, duplicate descriptor methods, 260 getownpropertydescriptor() methods, 261 prototype proxy, function of, purpose of two sets of methods, validating properties using, trim() method, 28 type coercion, typed arrays, array buffers, creating, manipulating with views, element size, 206 numeric data types, 199 regular arrays versus, 207 behavioral differences between, iterators, 208 methods in common, methods missing from typed arrays, methods present in typed arrays, 211 of() and from() methods, typeof operator, 6 7, 36, 101 U u flag, Uint8Array constructor, 204 Uint8ClampedArray constructor, 204 Uint16Array constructor, 204 Uint32Array constructor, 204 unhandledrejection event, unhandledrejection event, Unicode support, codepointat() method, identifiers, normalize() method, String.fromCodePoint() method, 16 u flag, UTF-16 code points, 14 15, 18 unnamed parameters, in ECMAScript 5, rest parameters, Index 321

12 unsettled promises, 217, unshift() method, 210 UTF-16 code points, 14 15, 18 V valueof() method, 111 values() iterator, , 176, value variable, 2 4, 6 var declarations, 2 3 in global scope, in loops, 7 8 views, manipulating array buffers with, W WeakMap constructor, 133 weak maps, initializing, 133 limitations of, 136 methods for, private object data, using, weak references, 127 WeakSet constructor, weak sets, creating, regular sets versus, WebGL, well-known symbols, 105 window object, 11 with statements, workers, 296 writefile() function, 216 Y y flag, yield keyword, , 157, Index

Symbols. accessor properties, attributes, creating, adding properties, 8 anonymous functions, 20, 80

Symbols. accessor properties, attributes, creating, adding properties, 8 anonymous functions, 20, 80 Index Symbols { } (braces) for function contents, 18 and object properties, 9 == (double equals operator), 5 === (triple equals operator), 5 [ ] (square brackets) for array literals, 10 for property access,