104 lines
1.6 KiB
Markdown
104 lines
1.6 KiB
Markdown
---
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title: JavaScript Arrays
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category: JavaScript
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---
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### Arrays
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```bash
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list = [a,b,c,d,e]
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```
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{: .-setup}
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```bash
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list[1] // → b
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list.indexOf(b) // → 1
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list.lastIndexOf(b) // → 1
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list.includes(b) // → true
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```
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### Subsets
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#### Immutable
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```bash
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list.slice(0,1) // → [a ]
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list.slice(1) // → [ b,c,d,e]
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list.slice(1,2) // → [ b ]
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```
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#### Mutative
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```bash
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re = list.splice(1) // re = [b,c,d,e] list == [a]
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re = list.splice(1,2) // re = [b,c] list == [a,d,e]
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```
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### Adding items
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#### Immutable
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```bash
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list.concat([X,Y]) // → [_,_,_,_,_,X,Y]
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```
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#### Mutative
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```bash
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list.push(X) // list == [_,_,_,_,_,X]
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list.unshift(X) // list == [X,_,_,_,_,_]
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list.splice(2, 0, X) // list == [_,_,X,_,_,_]
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```
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### Inserting
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```bash
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// after -- [_,_,REF,NEW,_,_]
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list.splice(list.indexOf(REF)+1, 0, NEW))
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```
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```bash
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// before -- [_,_,NEW,REF,_,_]
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list.splice(list.indexOf(REF), 0, NEW))
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```
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### Replace items
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```bash
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list.splice(2, 1, X) // list == [a,b,X,d,e]
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```
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### Removing items
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```bash
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list.pop() // → e list == [a,b,c,d]
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list.shift() // → a list == [b,c,d,e]
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list.splice(2, 1) // → [c] list == [a,b,d,e]
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```
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### Iterables
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```bash
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.filter(n => ...) => array
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```
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```bash
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.forEach(n => ...)
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```
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```bash
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.find(n => ...) // es6
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.findIndex(...) // es6
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```
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```bash
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.every(n => ...) => Boolean // ie9+
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.some(n => ..) => Boolean // ie9+
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```
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```bash
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.map(n => ...) // ie9+
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.reduce((total, n) => total) // ie9+
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.reduceRight(...)
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```
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