20个实用的JavaScript代码片段，助你成为更好的开发者

const getValue = (obj, path) => path
   .replace(/\[([^[\]]*)]/g, '.$1.')
   .split('.')
   .filter(prop => prop !== '')
   .reduce((prev, next) => (
       prev instanceof Object ? prev[next] : undefined
   ), obj);
getValue({ a: { b: c: 'd' } }, 'a.b.c'); // = d
getValue({ a: { b: c: [1, 2] } }, 'a.b.c[1]'); // = 2
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const clamp = (min, max, value) => {
 if (min > max) throw new Error('min cannot be greater than max');
 return value < min
   ? min
   : value > max
     ? max
     : value;
 }
}
clamp(0, 10, -5); // = 0
clamp(0, 10, 20); // = 10
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const sleep = async (duration) => (
 new Promise(resolve =>
   setTimeout(resolve, duration)
 )
);
await sleep(1000); // waits 1 sec
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const groupBy = (fn, list) => (
 list.reduce((prev, next) => ({
   ...prev,
   [fn(next)]: [...(prev[fn(next)] || []), next]
 }), {})
);
groupBy(vehicle => vehicle.make, [
 { make: 'tesla', model: '3' },
 { make: 'tesla', model: 'y' },
 { make: 'ford', model: 'mach-e' },
]);
// {  
//   tesla: [ { make: 'tesla', ... }, { make: 'tesla', ... } ],
//   ford: [ { make: 'ford', ... } ],
// }
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import groupBy from './groupBy';
const collectBy = (fn, list) =>  
 Object.values(groupBy(fn, list));
collectBy(vehicle => vehicle.make, [
 { make: 'tesla', model: '3' },
 { make: 'tesla', model: 'y' },
 { make: 'ford', model: 'mach-e' },
]);
// [  
//   [ { make: 'tesla', ... }, { make: 'tesla', ... } ],
//   [ { make: 'ford', ... } ],
// ]
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const head = list => list[0];
head([1, 2, 3]); // = 1
head([]); // = undefined
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const tail = list => list.slice(1);
tail([1, 2, 3]); // = [2, 3]
tail([]); // = []
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const flatten = list => list.reduce((prev, next) => ([
 ...prev,
 ...(Array.isArray(next) ? flatten(next) : [next])
]), []);
flatten([[1, 2, [3, 4], 5, [6, [7, 8]]]]); // = [1, 2, 3, 4, 5, 6, 7, 8]
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const intersectionBy = (fn, listA, listB) => {
 const b = new Set(listB.map(fn);
 return listA.filter(val => b.has(fn(val)));
};
intersectionBy(v => v, [1, 2, 3], [2, 3, 4]); // = [2, 3]
intersectionBy(v => v, [{ a: 1 }, { a: 2 }], [{ a: 2}, { a: 3 }, { a: 4 }]); // = [{ a: 2 }];
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const indexBy = (fn, list) =>
 list.reduce((prev, next) => ({
   ...prev,
   [fn(next)]: next
 }, {});
indexBy(val => val.a, [{ a: 1 }, { a: 2 }, { a: 3 }]);  
// = { 1: { a: 1 }, 2: { a:2 }, 3: { a: 3 } }
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import indexBy from './indexBy';
const differenceBy = (fn, listA, listB) => {
 const bIndex = indexBy(fn, listb);
 return listA.filter(val => !bIndex[fn(val)]);
});
differenceBy(val => val, [1,2,3], [3,4,5]); // = [1,2]
differenceBy(
  vehicle => vehicle.make,  
  [{ make: 'tesla' }, { make: 'ford' }, { make: 'gm' }],  
  [{ make: 'tesla' }, { make: 'bmw' }, { make: 'audi' }],  
); // = [{ make: 'ford' }, { make: 'gm' }]
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const recoverWith = async (defaultValue, fn, ...args) => {
 try {
   const result = await fn(...args);
   return result;
 } catch (_e) {
   return defaultValue;
 }
}
recoverWith('A', val => val, 'B'); // = B
recoverWith('A', () => { throw new Error() }); // = 'A'
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const distance = ([x0, y0], [x1, y1]) => (
 Math.hypot(x1 - x0, y1 - y0)
);
distance([0, 1], [5, 4]); // = 5.8309518948453
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const dropWhile = (pred, list) => {
 let index = 0;
 list.every(elem => {
   index++;
   return pred(elem);
 });
 return list.slice(index-1);
}
dropWhile(val => (val < 5), [1,2,3,4,5,6,7]); // = [5,6,7]
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const sumBy = (fn, list) =>
 list.reduce((prev, next) => prev + fn(next), 0);
sumBy(product => product.price, [
  { name: 'pizza', price: 10 },  
 { name: 'pepsi', price: 5 },
 { name: 'salad', price: 5 },
]); // = 20
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const ascending = (fn) => (a, b) => {
 const valA = fn(a);
 const valB = fn(b);
 return valA < valB ? -1 : valA > valB ? 1 : 0;
}
const byPrice = ascending(val => val.price);
[{ price: 300 }, { price: 100 }, { price: 200 }].sort(byPrice);  
// = [{ price: 100 }, { price: 200 }, { price: 300 }]
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const descending = (fn) => (a, b) => {
 const valA = fn(b);
 const valB = fn(a);
 return valA < valB ? -1 : valA > valB ? 1 : 0;
}
const byPrice = descending(val => val.price);
[{ price: 300 }, { price: 100 }, { price: 200 }].sort(byPrice);  
// = [{ price: 300 }, { price: 200 }, { price: 100 }]
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const findKey = (predicate, index) => Object
 .keys(index)
 .find(key => predicate(index[key], key, index));
findKey(
 car => !car.available,
 {
   tesla: { available: true },
   ford: { available: false },
   gm: { available: true }
 },
); // = "ford"
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const bifurcateBy = (predicate, list) =>
 list.reduce((acc, val, i) => (
    acc[predicate(val, i) ? 0 : 1].push(val), acc),  
   [[], []]
 );
bifurcateBy(val => val > 0, [-1, 2, -3, 4]);  
// = [[2, 4], [-1, -3]]
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const pipe = (functions, ...args) => (
 functions.reduce(
   (prev, next) => Array.isArray(prev) ? next(...prev) : next(prev),
   args
)
);
pipe([Math.abs, Math.floor, val => -val], 4.20); // = -4
pipe([(a, b) => a - b, Math.abs], 5, 10); // = 5
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