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摘要： JavaScript const countOccurrences = (arr, val) => arr.reduce((a, v) => (v val ? a + 1 : a), 0) Examples countOccurrences([1, 1, 2, 1, 2, 3], 1) // 3 阅读全文

摘要： JavaScript const intersection = (a, b) => { const s = new Set(b) return [...new Set(a)].filter(x => s.has(x)) } Examples intersection([1, 2, 3], [4, 3 阅读全文

摘要： JavaScript const nthElement = (arr, n = 0) => (n -1 ? arr.slice(n) : arr.slice(n, n + 1))[0] Examples nthElement(['a', 'b', 'c'], 1) // 'b' nthElement 阅读全文

摘要： JavaScript const without = (arr, ...args) => arr.filter(v => !args.includes(v)) Examples without([2, 1, 2, 3], 1, 2) // [3] 阅读全文

摘要： JavaScript const firstN = (arr, n) => arr.slice(0, n) Examples firstN(['a', 'b', 'c', 'd'], 2) // ['a', 'b'] 阅读全文

摘要： JavaScript const lastN = (arr, n) => arr.slice(-n) Examples lastN(['a', 'b', 'c', 'd'], 2) // ['c', 'd'] 阅读全文

摘要： JavaScript const uniqueElements = arr => [...new Set(arr)] Examples uniqueElements([1, 2, 2, 3, 4, 4, 5]) // [1, 2, 3, 4, 5] 阅读全文

摘要： JavaScript const hasDuplicates = arr => new Set(arr).size !== arr.length Examples hasDuplicates([0, 1, 1, 2]) // true hasDuplicates([0, 1, 2, 3]) // f 阅读全文

摘要： JavaScript const castArray = val => (Array.isArray(val) ? val : [val]) Examples castArray('foo') // ['foo'] castArray([1]) // [1] 阅读全文

摘要： JavaScript const includesAll = (big, small) => small.every(s => big.includes(s)) Examples includesAll([1, 2, 3, 4], [1, 4]) // true includesAll([1, 2, 阅读全文