68 lines
1.4 KiB
Markdown
68 lines
1.4 KiB
Markdown
---
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title: JavaScript arrays
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category: JavaScript
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---
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## JavaScript arrays
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array = [a,b,c,d,e]
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array[1] //=> b
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array.indexOf(b) //=> 1
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### Subsets
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array.slice(0,1) //=> [a]
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array.slice(1) //=> [b,c,d,e]
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array.slice(1,2) //=> [b]
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// Destructive
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re = array.splice(1) // re = [b,c,d,e] array == [a]
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re = array.splice(1,2) // re = [b,c] array == [a,d,e]
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### Adding items
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array.push(X) // array == [_,_,_,_,_,X]
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array.unshift(X) // array == [X,_,_,_,_,_]
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array.splice(2, 0, X) // array == [_,_,X,_,_,_]
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array.concat([X,Y]) //=> [_,_,_,_,_,X,Y]
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### Inserting
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// after -- [_,_,REF,NEW,_,_]
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array.splice(array.indexOf(REF)+1, 0, NEW))
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// before -- [_,_,NEW,REF,_,_]
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array.splice(array.indexOf(REF), 0, NEW))
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### Replace items
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array.splice(2, 1, X) // array == [a,b,X,d,e]
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### Removing items
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array.pop() //=> e array == [a,b,c,d]
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array.shift() //=> a array == [b,c,d,e]
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array.splice(2, 1) //=> [c] array == [a,b,d,e]
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### Iterables
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.filter(n => ...) => Array
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.find(n => ...) // es6
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.findIndex(...) // es6
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.every(n => ...) => Boolean // ie9+
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.some(n => ..) => Boolean // ie9+
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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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