73 lines
1.2 KiB
Markdown
73 lines
1.2 KiB
Markdown
`undefined` predicates are ignored and `undefined` is returned if all predicates are `undefined`, this permits the most efficient composition:
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```js
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const compositePredicate = not(every(undefined, some(not(predicate2), undefined)))
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// ends up as
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const compositePredicate = predicate2
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```
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Predicates can also be passed wrapped in an array:
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```js
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const compositePredicate = every([predicate1, some([predicate2, predicate3])])
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```
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`this` and all arguments are passed to the nested predicates.
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### `every(predicates)`
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> Returns a predicate that returns `true` iff every predicate returns `true`.
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```js
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const isBetween3And7 = every(
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n => n >= 3,
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n => n <= 7
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)
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isBetween3And10(0)
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// → false
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isBetween3And10(5)
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// → true
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isBetween3And10(10)
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// → false
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```
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### `not(predicate)`
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> Returns a predicate that returns the negation of the predicate.
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```js
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const isEven = n => n % 2 === 0
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const isOdd = not(isEven)
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isOdd(1)
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// true
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isOdd(2)
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// false
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```
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### `some(predicates)`
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> Returns a predicate that returns `true` iff some predicate returns `true`.
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```js
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const isAliceOrBob = some(
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name => name === 'Alice',
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name => name === 'Bob'
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)
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isAliceOrBob('Alice')
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// → true
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isAliceOrBob('Bob')
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// → true
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isAliceOrBob('Oscar')
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// → false
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```
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