44:["$","title",null,{"children":"What the ... JS Pt. 6 | Jing D | Observable"}] 4c:Tbf6,md` | Method Name | Object | Reflect| | --- | --- | --- | | defineProperty() | returns the object that was passed to the function if successful, raise TypeError if failed to create property. | returns true if successful and false otherwise.| | defineProperties() | same as above | N/A | | set() | N/A | returns boolean based on if operation was successful. *Throws a TypeError* if the target was not an Object. | | get() | N/A | returns boolean based on if operation was successful. *Throws a TypeError* if the target was not an | | deleteProperty() | N/A | returns boolean based on if operation was successful | | getOwnPropertyDescriptor() |returns a property descriptor of the given property if it exists on the object argument passed in, and returns undefined if it does not exist. However, if an object is not passed in as the first argument, it will be coerced into an object. | returns a property descriptor of the given property if it exists on the object and undefined if it does not. *Throw a TypeError* if anything other than an object (a primitive) is passed in as the first argument.| |getOwnPropertyDescriptors() | returns an object containing a property descriptor of each passed-in object. Returns an empty object if the passed-in object has no owned property descriptors. | N/A | | getPrototypeOf() | returns the prototype of the given object. Returns null if there are no inherited properties. coerces non-objects | returns the prototype of the given object. Returns null if there are no inherited properties, and *throws a TypeError* for non-objects. | |setPrototypeOf()| returns the object itself if its prototype was set successfully. Throws a TypeError if the prototype being set was anything other than an Object or null, or if the prototype for the object being modified is non-extensible.| returns true if the prototype was successfully set on the object and false otherwise. *Throws a TypeError* if the target passed in was not an Object, or if the prototype was anything other than an Object or null.| |isExtensible()|returns true if the object is extensible, and false otherwise. If the first argument is not an object (a primitive), it will be coerced into a non-extensible, ordinary object and return false.|returns true if the object is extensible, and false if it is not. *Throws a TypeError* if the first argument is not an object (a primitive).| | preventExtensions() | returns the object that is being made non-extensible. If the argument is not an object (a primitive) treats the argument as a non-extensible, ordinary object and returns the object itself.|returns true if the object has been made non-extensible, false otherwise. *Throws a TypeError* if the argument is not an object (a primitive).| |keys() | returns an Array of strings that map to the target object's own (enumerable) property keys. If the target is not an object, coerces into objects| N/A| |ownKeys()| N/A | returns an Array of property names that map to the target object's own property keys. *Throws a TypeError* if the target is not an Object.|`4d:T5f2,md` | Handler / trap | Interceptions | Invariants | | --- | --- | --- | | getPrototypeOf() | Object.getPrototypeOf(), Reflect.getPrototypeOf(),__ proto __ ,Object.prototype.isPrototypeOf(),instanceof | If target is not extensible, Object.getPrototypeOf(proxy) method must return the same value as Object.getPrototypeOf(target). | | setPrototypeOf() | Object.setPrototypeOf(), Reflect.setPrototypeOf() | | | isExtensible()| Object.isExtensible(), Reflect.isExtensible() | must return the same value as Object.isExtensible(target). | preventExtensions() | Object.preventExtensions(), Reflect.preventExtensions() | returns true if Object.isExtensible(proxy) is false. | | getOwnPropertyDescriptor() | Object.getOwnPropertyDescriptor(),Reflect.getOwnPropertyDescriptor() | must return an object or undefined | | defineProperty() | Object.defineProperty(), Reflect.defineProperty() | must adhere to property's configurable policy | |has() | Reflect.has() | | | get() | Reflect.get() | behavior need to adhere to property property | | set() | | | | deleteProperty() | delete proxy[prop], delete proxy.prop, Reflect.deleteProperty()| cannot delete non-configurable property | | enumerate() | Reflect.enumerate() | | | ownKeys() | Object.getOwnPropertyNames(), Object.getOwnPropertySymbols(), Object.keys(), Reflect.ownKeys() | | | apply()|proxy(..args), Function.prototype.apply() and Function.prototype.call(), Reflect.apply() | | | construct() | new proxy(...args), Reflect.construct()| |
### Static Method `4e:[] 48:{"id":"bb75ab4cd786b5f6","slug":"what-the-js-pt-5","title":"What the ... JS Pt. 6","thumbnail":"3743a06a60c8118b008d2c2a8a0aa76dc9e2fc5f045076bd6a26432e5c0f0040","access_level":"public","create_time":"$D2020-08-18T19:30:20.393Z","update_time":"$D2020-09-01T03:25:48.249Z","view_time":null,"first_public_time":"$D2020-08-18T22:25:50.244Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"d10f468021cb6169","login":"mystiquepanda","name":"Jing D","avatar_url":"https://avatars-next.observableusercontent.com/4cf5309591931daa3113ac391031aae6cd78ac18089619fd39c4a77f8eefd07e","tier":"starter_2024","bio":"","followed_by_you":false,"follows_you":false},"version":240,"publish_version":240,"role":null,"authored":false,"authors":[{"type":"individual","id":"41f898cb9b136929","login":"mystiquepanda","name":"Jing D","avatar_url":"https://avatars-next.observableusercontent.com/4cf5309591931daa3113ac391031aae6cd78ac18089619fd39c4a77f8eefd07e","tier":null,"bio":"","followed_by_you":false,"follows_you":false}],"members":[{"type":"individual","id":"41f898cb9b136929","login":"mystiquepanda","name":"Jing D","avatar_url":"https://avatars-next.observableusercontent.com/4cf5309591931daa3113ac391031aae6cd78ac18089619fd39c4a77f8eefd07e","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":0,"collection":{"id":"bd861e327ed5fcab","slug":"what-the-js","title":"What the ... JS","owner":{"id":"d10f468021cb6169","login":"mystiquepanda","name":"Jing D"}},"type":"notebook","body":{"titling":"auto","title":"What the ... JS Pt. 6","cells":[{"id":0,"value":"md`# What the ... JS Pt. 6\n**[ Control abstraction objects ]**`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":180,"value":"toc({selector: \"h2,h3,h4,h5,h6\", heading: \"Table of Contents\"});","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":11,"value":"md`\n

\n## Promise\nCallbacks inside-out\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":14,"value":"//depends on which callback is called, the state of promise will change.\nnew Promise(\n (fulfilledCB,rejectedCB)=>{\n setTimeout(()=>{ rejectedCB();return \"done\"}, 3000);})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":19,"value":"md`State of Promise:\n- pending: initial state\n- fulfilled: operation completed successfully - \"resolved\"\n- rejected: operation failed.\n\n| Method | Description |\n| --- | --- |\n| .then(fulfilledCB[, rejectedCB]) | fulfilledCB(value), rejectedCB(reason) called asynchronously| \n| .catch(error) | same as .then(null,fail) |\n| .finally() | |\n
`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":23,"value":"Promise.reject()\n .then(() => 100, () => -100)\n .then(solution => ('Resolved with ' + solution))","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":26,"value":"// doesn't error even when CB aren't valid\nPromise.resolve().then({jibberish:true})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"//async execution\n{\nlet resolvedProm = Promise.resolve(33);\nreturn resolvedProm.then(value => {\n return \"called after the end of the main stack. the value received and returned is: \" + value;\n});\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":32,"value":"{\n let arr=[];\n let resolvedProm = Promise.resolve(33);\n let thenProm = resolvedProm.then(value => {\n arr.push(\"called after the end of the main stack. the value received and returned is: \" + value);\n return value;\n});\n let t = setTimeout(() => {\n arr.push(\"until after timeout\",thenProm);\n });\n arr.push([\"instant\",thenProm]);\n\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":43,"value":"{\n let arr = [];\n Promise.resolve('dinosaurs')\n .then(s=>{\n return new Promise(function(res, rej) {\n setTimeout(function() {\n s += ' rule';\n res(s);\n }, 1);\n });\n })\n .then(s=>{\n setTimeout(function() {\n s += 'D';\n arr.push([\"misconception: \",s]);\n }, 1)\n return s;\n }) \n .then(s=>{\n arr.push(\"Listen! \");\n arr.push([\"fact:\",s]);\n })\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":51,"value":"//order matters with exception handling\n{\n let arr = [];\n Promise.resolve()\n .then(() => {\n throw new Error('Kaboom!');\n })\n .catch(e => {\n arr.push('Fire!Fire! ' + e.message);\n })\n .then(() => {\n arr.push(\"Looks like all good now\");\n });\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":53,"value":"{\n /* returns another pending promise object, the resolution/rejection of the promise returned by then will be subsequent to the resolution/rejection of the promise returned by the handler */\n let arr = [];\n let rej = Promise.reject();\n let p = new Promise((s,r)=>{setInterval(s,1000)}).then(s=>{return rej},r=>{}).then(s=>arr.push(\"success!\"),r=>arr.push(\"rejected!\"));\n\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":57,"value":"md`\n
\n### Error Handling\n\nWhen a Promise fails one of the two events (type: PromiseRejectionEvent) are sent to global scope\n- rejectionhandled\n- unhandledrejection\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":64,"value":"{\n let arr = []\n globalThis.onunhandledrejection = e => arr.push(\"globally heard a unhandled rejection from promise \",e)\n globalThis.onrejectionhandled = e => arr.push(\"globally heard a rejection from promise \",e)\n let p = await new Promise((s,r)=>{r(\"no good reason\")}).then(()=>{arr.push(\"this won't print\")})\n}\n//This doesn't seem to work well in Observable","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":76,"value":"md`\n
\n### Static methods\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":80,"value":"{\n let arr = [];\n let p1 = Promise.resolve(\"uno\");\n let p2 = \"dos\";\n let p3 = new Promise((resolve, reject) => {\n setTimeout(() => {\n arr.push(\"done with p3\")\n resolve(\"tres\");\n }, 3000);\n }); \n setTimeout(\n ()=>{\n arr.push(\"stack is empty\")\n Promise.all([p1,p2,p3]).then(res =>arr.push(\"async \", res))\n Promise.all([]).then(res => arr.push(\"empty iterator is sync\"))\n })\n \n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":83,"value":"// Fast fail\n{\n let arr = [];\n let p1 = new Promise((resolve, reject) => { \n setTimeout(() => resolve('ten sec'), 10000); \n }); \n let p2 = new Promise((resolve, reject) => { \n setTimeout(() => resolve('one sec'), 1000); \n });\n let pf = new Promise((resolve, reject) => {\n setTimeout(() => reject(new Error('reject, one.five sec')),1500);\n });\n Promise.all([p1, p2, pf])\n .then(v => arr.push(v))\n .catch(e => arr.push(e.message));\n \n return arr\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":86,"value":"// catching fails \n{\n let arr = [];\n let p1 = new Promise((resolve, reject) => { \n setTimeout(() => resolve('ten sec'), 10000); \n }); \n let p2 = new Promise((resolve, reject) => { \n setTimeout(() => resolve('one sec'), 1000); \n });\n let pf = new Promise((resolve, reject) => {\n setTimeout(() => reject(new Error('reject, one.five sec')),1500);\n });\n Promise.all([p1,p2,pf.catch(e => e),]).then(values => { \n arr.push(values[0]) // \"p1_delayed_resolution\"\n arr.push(values[1])\n arr.push(values[2]) // \"Error: p2_immediate_rejection\"\n })\n \n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":91,"value":"{\n let arr = [];\n let p1 = Promise.resolve(\"uno\");\n let p2 = \"dos\";\n let p3 = new Promise((resolve, reject) => {\n setTimeout(() => {\n arr.push(\"done with p3\")\n resolve(\"tres\");\n }, 3000);\n }); \n setTimeout(\n ()=>{\n arr.push(\"stack is empty\")\n Promise.allSettled([p1,p2,p3]).then(res =>arr.push(\"async \", res))\n })\n \n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":94,"value":"{\n let arr = [];\n let p1 = new Promise((s,r) => setTimeout(s, 500, 'one'))\n let p2 = new Promise((s,r) => setTimeout(s, 1000, 'two'))\n Promise.race([p1, p2]).then(v => arr.push(v));\n \n return arr\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":96,"value":"{\n let arr = [];\n let p1 = new Promise((s,r) => s(\"one\"))\n let p2 = new Promise((s,r) => setTimeout(s, 1000, 'two'))\n Promise.race([p1, p2]).then(v => arr.push(v));\n \n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":98,"value":"Promise.race([]).then(v => v);\n// pending promise","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":105,"value":"{\n let arr = [];\n let forever = Promise.race([]);\n let fulfilled = Promise.resolve(100);\n\n let p = Promise.race([forever, fulfilled, \"non-Promise value\"]);\n let p2 = Promise.race([forever, \"non-Promise value\", fulfilled]);\n arr.push([p,p2]);\n setTimeout(function(){\n arr.push('the stack is now empty');\n arr.push([\"p: \", p]);\n arr.push([\"p2: \", p2]);\n });\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":110,"value":"md`\n

\n## AsyncFunction\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":118,"value":"Object.getPrototypeOf(async function(){})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":121,"value":"{\n let arr = [];\n function after2Seconds() {\n return new Promise(resolve => {\n setTimeout(() => {\n resolve('resolved');\n }, 2000);\n });\n }\n\n async function asyncCall() {\n arr.push('calling:');\n const result = await after2Seconds();\n arr.push(result);\n }\n\n asyncCall();\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":123,"value":"// async function always returns a promise\n{\n let arr = [];\n arr.push((async () => (1))());\n return arr\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":129,"value":"{\n let arr = [];\n async function f() {\n const result1 = await new Promise((resolve) => setTimeout(() => resolve('1'),3000))\n arr.push((\"result1: \",result1)); \n const result2 = await new Promise((resolve) => setTimeout(() => resolve('2')))\n arr.push((\"result2: \",result2));\n }\n f();\n arr.push(\"this is the end\");\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":132,"value":"//use Promise.all or Promise.allSettled when dealing with multiple promise\n{\n let arr = [];\n let f = async () => {\n const p1 = new Promise((s) => setTimeout(() => s('1'), 2000))\n const p2 = new Promise((_,r) => setTimeout(() => r('2'), 500)) \n const results = [await p1, await p2] \n }\n arr.push( f().catch(() => {}) )\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":136,"value":"// parallel execution\n{\n let arr = [];\n let slow = () => {\n arr.push(\"start slow..\");\n return new Promise(s=>{setTimeout(()=>s(\"slow done\"),5000)});\n }\n let fast = () => {\n arr.push(\"start fast..\");\n return new Promise(s=>{setTimeout(()=>s(\"fast done\"),3000)});\n }\n let parallel = async () => {\n await Promise.all([\n (async()=>arr.push(await slow()))(),\n (async()=>arr.push(await fast()))()\n ])\n arr.push(\"all done\")\n }\n parallel()\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":141,"value":"md`\n

\n## Reflect\n#ES2015\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":147,"value":"Function.prototype.apply.call(Math.floor, undefined, [1.75]);","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":150,"value":"Reflect.apply(Math.floor, undefined, [1.75]);","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":152,"value":"$4c","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":142,"value":"md`\n

\n## Proxy\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":155,"value":"{\n let target = {\n k: \"basic\",\n tbr: \"special\"\n };\n let handler = {\n get: function(target, prop) {\n return prop in target? target[prop] : \"magic\"\n }\n };\n\n let p = new Proxy(target, handler);\n return [p.k,p.new];\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":157,"value":"{\n let target = {\n k: \"basic\",\n tbr: \"special\"\n };\n let refHandler = {\n get: function(target, prop, receiver){ \n return prop === \"tbr\" ? \"replaced value\": Reflect.get(...arguments)\n }\n }\n let p = new Proxy(target, refHandler);\n return [p.k,p.tbr];\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":160,"value":"$4d","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":165,"value":"{\n let target = {\n k: \"basic\",\n tbr: \"special\"};\n \n let revocable = Proxy.revocable(target, {\n get: function(target, prop) {\n return prop in target? \"[[\" + Reflect.get(...arguments) + \"]]\" : \"proxy magic\" ;\n }\n });\n return revocable.proxy.nonexisting;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":168,"value":"{\n let target = {\n k: \"basic\",\n tbr: \"special\"};\n \n let revocable = Proxy.revocable(target, {\n get: function(target, prop) {\n return prop in target? \"[[\" + Reflect.get(...arguments) + \"]]\" : \"proxy magic\" ;\n }\n });\n revocable.revoke();\n return revocable.proxy.nonexisting;\n // same error for the following\n //revocable.proxy.foo = 1;\n //delete revocable.proxy.foo;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":170,"value":"md`**Use Case: Validation**`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":175,"value":"{\n let validator = {\n set: function(obj, prop, value) {\n if (prop === 'age') {\n if (!Number.isInteger(value)) {\n throw new TypeError('The age is not an integer');\n }\n if (value > 200) {\n throw new RangeError('The age seems invalid');\n }\n }\n obj[prop] = value;\n return true;\n }\n };\n\n let person = new Proxy({}, validator);\n person.age = 'young';\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":177,"value":"md`\nother use cases:\n- Extending constructor\n- Manipulating DOM nodes\n- Value correction and an extra property\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":187,"value":"md`\n

\n## Generators\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":191,"value":"{\n let generator = function* () { \n yield 1;\n yield \"two\";\n yield 3n;\n return false;\n }\n let g = generator();\n return [g.next(),g.next(),g.next(), g.next()]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":194,"value":"{\n let arr = [];\n function* fibonacci() {\n const f = [];\n const base = function*() {\n yield f.push(0)-1; \n yield f.push(1)-1;\n };\n\n yield* base();\n while (true) {\n const {length:l} = f;\n f.push(f[l-2]+f[l-1]);\n yield f[l];\n }\n }\n let f = fibonacci();\n for (let i =0; i < 5; i++) {\n arr.push(f.next().value);\n }\n f.return();\n arr.push(f.next().value);\n \n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":197,"value":"{\n let arr = [];\n function* fibonacci() {\n let f = [0,1];\n yield* f;\n while (true) {\n const {length:l} = f;\n f.push(f[l-2]+f[l-1]);\n yield f[l];\n }\n }\n\n function* gen(){\n let inner = function*() {\n yield* [1,2];\n return \"inner done\";\n }\n yield* (yield* inner());\n return \"done\";\n }\n let g = gen();\n for (let i =0; i < 20; i++) {arr.push(g.next())}\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":200,"value":"{\n let arr = [];\n const con = Object.getPrototypeOf(function*(){}).constructor;\n const g = new con('let vals=[1,2]; yield* vals');\n const iterator = g();\n let i;\n do{\n i = iterator.next(); \n arr.push(`from generator ${i.value}`)\n }while(!i.done); \n \n return arr;\n }\n","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":202,"value":"{\n let arr = [];\n function* gen(i){\n arr.push(`print ${i}`);\n const j = 5*(yield(i*10));\n arr.push(`print ${j}`);\n const k = yield(2*j/4);\n arr.push(`print ${k}`);\n return(i+j+k);\n }\n let g = gen(10);\n g.next(20);\n g.next(10);\n g.next(5);\n\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":217,"value":"md`\n

\n## Iterators\n| protocol | property | |\n| --- | --- | --- |\n| Iterable | [Symbol.iterator] | A zero-argument function that returns an 'Iterator' object|\n| Iterator | next() | a zero-argument function that return {value:,done:boolean}|\n\nA generator object is both *iterator* and *iterable*\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":220,"value":"{\n let weekdays = new String(\"monday to friday\");\n weekdays[Symbol.iterator] = function* () {\n yield* ['m','t','w','th','f'];\n };\n return [[...weekdays],weekdays+\"\"];\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":224,"value":"{\n let weekdays = new String(\"monday to friday\");\n weekdays[Symbol.iterator] = function () {\n return {\n next: function () {\n return this._first ? {\n value: 'no weekend',\n done: (this._first = false)\n } : {\n done: true\n }\n },\n _first: true\n };\n };\n return [...weekdays]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":230,"value":"//#ES2015 class syntax\n{\n class WeekClass {\n *[Symbol.iterator]() {\n yield* ['m','t','w','th','f'] \n }\n }\n return [...new WeekClass()]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":5,"value":"md`\n
\n# Appendix`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":7,"value":"import {toc} from \"@harrystevens/toc\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W4e","stdlib":"1"}} 24:null