44:["$","title",null,{"children":"What the ... JS Pt. 4 | Jing D | Observable"}] 4c:[] 48:{"id":"702a58c6b6d16dee","slug":"what-the-js-pt-4","title":"What the ... JS Pt. 4","thumbnail":"d1f3a1098aa6313992542fe8ee001e9bfdaaf2cef795a440622e1bf4013b450e","access_level":"public","create_time":"$D2020-08-17T21:47:09.741Z","update_time":"$D2020-09-01T02:55:33.147Z","view_time":null,"first_public_time":"$D2020-08-18T20:12:53.013Z","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":352,"publish_version":352,"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. 4","cells":[{"id":0,"value":"md`# What the ... JS Pt. 4\n**[ Collections ]**`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":17,"value":"toc({selector: \"h2,h3,h4,h5,h6\", heading: \"Table of Contents\"});","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":10,"value":"md`\n
\n## Array\n
\n### static methods\nif it quacks (a value) looks like a duck (an array) then it is a duck (an array)?`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"Array.isArray(new Int8Array())","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":29,"value":"md`\n
\n// isArray Polyfill
\n\nif (!Array.isArray) {
\n Array.isArray = function(arg) {
\n return Object.prototype.toString.call(arg) === '[object Array]';
\n }\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":32,"value":"{\n let arrLike = {v:[1,2,3],[Symbol.iterator]:function*(){yield*this.v}};\n return Array.from(arrLike,x=>x+x)\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":40,"value":"Array.of(1, 2, 3, undefined);","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":43,"value":"md`\n
\n### Instance Method and properties\n
\n\n| instance method | output | note | \n| --- | --- | --- |\n| .map((item, index, array)=>{}),this) | Array | | \n| .every((item, index, array)=>{})) | boolean | |\n| .some((item, index, array)=>{},this) | boolean | |\n| .filter((item, index, array)=>{},this) | Array | |\n| .forEach(item, index, array)=>{},this) | void | | \n| .find(item, index, array)=>{},this) | item | | \n| .findIndex(item, index, array)=>{},this) | void | | \n| .reduce((accu, item, index, array)=>{},initAccu)| accu | Array[0] = initAccu if not provided, when initAccu isn't provided, iteration is called one less time than otherwise,excluding holes | \n| .reduceRight((accu, item, index, array)=>{},initAccu) | accu | excluding holes| \n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":54,"value":"{\n let arr = [...Array(5).keys()];\n arr.length=10;\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":57,"value":"{\n let arr = [...Array(5).keys()];\n arr.length=3;\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":59,"value":"{\n let holey = ['Hello'];\n holey[99] = 'world';\n return holey.length;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":66,"value":"{\n let arr = [];\n [1,3,,,'last',undefined,4].forEach((e) => arr.push(e));\n return arr;\n}\n// skips holes(exmpty) during iteration","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":79,"value":"{\n let arr = [5, 4, 100];\n let sum = 0;\n let sumFunction = async (a, b) => a+b;\n arr.forEach(async (r) => sum = await sumFunction(sum, r));\n return sum;\n}\n// callbacks within iteration need to be synchronous","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":86,"value":"[1,2,3].map((c,i,a)=>{a.push(101);return c>100})\n// iteration scope, defined on first iteration","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":91,"value":"[5, 4, 7, 11, 2, 6].filter( (e, index, arr) => {\n arr.pop()\n return e < 6\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":96,"value":"[5, 4, 7, 11, 2, 6].filter( (e, i, arr) => {\n arr[Math.min(i+1,arr.length-1)]+=10\n return e < 6\n})","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":98,"value":"[{x:22},{x:42},{x:-100}].map( e => e.x )\n.reduce(( max,cur) => Math.max( max, cur), -Infinity );","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":100,"value":"[100,\"abc\",new Boolean(false)].some(x=>!x)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":102,"value":"md`\n- **back**: .pop() , .push()\n- **front**: .shift(), .unshift()\n- **by index**: .splice(pos, n)\n- **shallow copy**: .slice()\n- **search**: .indexOf(), lastIndexOf()\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":105,"value":"['a', 'b', 'c'].concat(1, [2, 3]);","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":108,"value":"[1, 2, 3, 4, 5].copyWithin(-4)\n// like memmove","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":110,"value":"[1, 2, 3, 4, 5].copyWithin(0, 3)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":112,"value":"[1, 2, 3, 4, 5].copyWithin(0, 3, 4)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":114,"value":"[1, 2, 3, 4, 5].copyWithin(-2, -3)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":116,"value":"[].copyWithin.call({length: 5, 3: 1}, 0, 3)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":118,"value":"[1, 2, 3, 4, 5].fill(4, -3, -1)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":120,"value":"[1, 2, 3, 4, 5].fill(4, 3, 6)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":122,"value":"Array(5).fill(4)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":124,"value":"[].fill.call({ length: 3 }, 4)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":126,"value":"{\n let arr = Array(3).fill({});\n arr[0].clone = \"hi\";\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":131,"value":"[1, 2, NaN].includes(NaN) ","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":134,"value":"md`\n
\n### Uniform Typed Array\n- Int8Array, Uint8Array, Uint8ClampedArray\n- Int16Array, Uint16Array\n- Int32Array, Uint32Array\n- Float32Array, Float64Array\n- BigInt64Array, BigUint64Array\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":138,"value":"md`\n
\n## Map\n#ES2015\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":154,"value":"{\n let m = new Map();\n m['random'] = false;\n m.set('random',true);\n m.set(NaN,\"notANumber\")\n m.set(undefined,\"undef\")\n m.set(null,\"hasValue?\")\n m.set(Symbol.for(\"special\"),true)\n return [m.get(NaN),m.get(undefined),m.get(null),m.get(Symbol.for(\"special\")),m.get(Number(\"broken\"))]\n}\n//insertion order are perserved when iterating","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":160,"value":"new Map().size=3\n//under strict mode, it throws exception","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":163,"value":"{\n let original = new Map([[1, {id:'one'}]]);\n let clone = new Map(original);\n return original === clone;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":169,"value":"{\n let original = new Map([[1, {id:'one'}]]);\n let clone = new Map(original);\n original.get(1)[\"name\"]='one';\n clone.get(1);\n return clone;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":171,"value":"{\n let first = new Map([\n [1, 'one'],\n [2, 'two'],\n [3, 'three'],\n ]);\n let second = new Map([\n [1, 'uno'],\n [2, 'dos']\n ]);\n return new Map([...first, ...second, [1, 'eins']]);\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":141,"value":"md`\n
\n## Set\n#ES2015\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":173,"value":"{\n let s = new Set();\n s.add({});\n s.add({});\n s.add(null);\n s.add(undefined);\n\n let arr = [];\n for (let [key, value] of s.entries()){\n arr.push({key,value})\n }\n\n return arr;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":179,"value":"{\n let s1 = new Set([1, 2, 3, 4]);\n let s2 = new Set([2, 4, 6, 8, 9]);\n let intersection = new Set([...s1].filter(x => s2.has(x)));\n let difference = new Set([...s1].filter(x => !s2.has(x)));\n return [intersection, difference];\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":183,"value":"(new Set([NaN,undefined,null,,NaN])).has(NaN)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":145,"value":"md`\n
\n## Weakmap\n#ES2015\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":189,"value":"new WeakMap().set(1,\"one\")","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":191,"value":"new WeakMap().set(globalThis,1)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":194,"value":"md`\n
\n*Use case*: Hide Implementation`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":198,"value":"{\n const privates = new WeakMap();\n\n function Public() {\n const me = {\n // Private data goes here\n };\n privates.set(this, me);\n }\n\n Public.prototype.method = function () {\n const me = privates.get(this);\n // Do stuff with private data in 'me'...\n }\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":147,"value":"md`\n
\n## Weakset\n#ES2015\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":202,"value":"new WeakSet().add(1);\n//cannot hold primitive","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":204,"value":"new WeakSet().add({});","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":208,"value":"md`\n
\n*Use case*: Detecting circular references\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":211,"value":"function execRecursively(fn, subject, _refs = null){\n if(!_refs)\n _refs = new WeakSet();\n\t\n // Avoid infinite recursion\n if(_refs.has(subject))\n return;\n\n fn(subject);\n if(\"object\" === typeof subject){\n _refs.add(subject);\n for(let key in subject)\n execRecursively(fn, subject[key], _refs);\n }\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":230,"value":"md`\n
\n## Destructuring\n
\n### Object\n
\nfor object destructuring, the right hand need to be coercible to an Object and destructuring is done by property name\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":274,"value":"{\n let { blowUp } = null;\n return blowUp\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":277,"value":"{\n let { blowUp } = undefined\n return blowUp\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":282,"value":"{\n let { blowUp } = Number(10);\n return blowUp\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":237,"value":"{\n let [a,oa,[[b,,c],...d]]=[1,{oa:\"one\"},[[3,4],[5,6]]];\n return [a,JSON.stringify(oa),b,c,d.toString()]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":258,"value":"{\n // rename destructured object variables and default values \n let {oa:na=\"uno\",ob:nb=\"dos\"}={oa:\"one\"}\n return [na,nb]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":261,"value":"{\n // you can destructure from any level of the object\n let o = {random:true};\n Object.setPrototypeOf(o,{hidden:\":)\"});\n let {random:r,hidden,missing} = o;\n \n return [missing, hidden]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":301,"value":"md`\n
\n### Array\n
\nfor array destructuring, the right hand need to be iterable.\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":279,"value":"{\n let [a,b] = Number(10)\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":232,"value":"{\n // the \"shape\" need to match in order to destructure array\n let [a,,[[b,,c],...d]]=[1,[[3,4],[5,6]]]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":308,"value":"{\n // default value\n let [a,[[b=-100,,c=-100],...d]]=[1,[[3,4],[5,6]]];\n return [b,c]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":339,"value":"md`\n**use case:**\nswapping two variables without an intermediate container variable`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":334,"value":"{\n let [x,y]=[\"x\",\"y\"];\n [y,x]=[x,y];\n return [x,y]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":342,"value":"md`\n**use case:** array clone`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":345,"value":"{\n const arr = [0,1,2,3];\n const copy = arr;\n const [...clone] = arr;\n copy[0] = 100\n clone[0] = -100;\n return JSON.stringify({arr,clone,copy})\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":316,"value":"md`\n
\n### Function\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":318,"value":"{\n let f=({a=1,b=2,c})=>{return{a,b}};\n f();\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":323,"value":"{\n let f=({a=1,b=2,c})=>{return{a,b}};\n let {a=100,b=200,c=300} = f(-100);\n return [a,b,c]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":330,"value":"{\n let f=({a=1,b=2,c})=>{return{a,b}};\n let {a=100,b=200,c=300} = f({b:\"neg 2\"});\n return [a,b,c]\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":6,"value":"md`\n
\n# Appendix`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","tool":"$undefined","providerMetadata":"$undefined","attachments":"$undefined","output":"$undefined","database":"$undefined"},{"id":2,"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":"$undefined"}],"files":"$W4c","stdlib":"1"}} 24:null