1、allEqual：检查数组各项相等
const allEqual = arr => arr.every(val => val === arr[0]);
allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true
2、approximatelyEqual：约等于
const approximatelyEqual = (v1, v2, epsilon = 0.001) => Math.abs(v1 - v2) < epsilon;
approximatelyEqual(Math.PI / 2.0, 1.5708); // true
3、castArray：其它类型转数组
castArray('foo'); // ['foo']
castArray([1]); // [1]
castArray(1); // [1]
4、compact：去除数组中的无效/无用值
const compact = arr => arr.filter(Boolean);
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]);
// [ 1, 2, 3, 'a', 's', 34 ]5、deepFlatten：递归扁平化数组
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]
6、intersection：两数组的交集
const intersection = (a, b) => {
const s = new Set(b);
return a.filter(x => s.has(x));
};
intersection([1, 2, 3], [4, 3, 2]); // [2, 3]7、capitalize：首字母大写
const capitalize = ([first, ...rest]) =>
first.toUpperCase() + rest.join('');
capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'
8、decapitalize：首字母小写
const decapitalize = ([first, ...rest]) =>
first.toLowerCase() + rest.join('')
decapitalize('FooBar'); // 'fooBar'
decapitalize('FooBar'); // 'fooBar'9、dayOfYear：当前日期天数
const dayOfYear = date =>
Math.floor((date - new Date(date.getFullYear(), 0, 0)) / 1000 / 60 / 60 / 24);
dayOfYear(new Date()); // 285
10、Get Days Between Dates：返回日期间的天数
const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
(dateFinal - dateInitial) / (1000 * 3600 * 24);
getDaysDiffBetweenDates(new Date('2019-01-01'), new Date('2019-10-14')); // 286
