我总是发现range
JavaScript 中缺少该函数,因为它在 python 和其他版本中可用?在 ES2015 中是否有任何简洁的方法来生成数字范围?
编辑:我的问题与提到的重复不同,因为它特定于 ES2015 而不是 ECMASCRIPT-5。此外,我需要范围从 0 开始,而不是特定的起始数字(尽管如果有它会很好)
我总是发现range
JavaScript 中缺少该函数,因为它在 python 和其他版本中可用?在 ES2015 中是否有任何简洁的方法来生成数字范围?
编辑:我的问题与提到的重复不同,因为它特定于 ES2015 而不是 ECMASCRIPT-5。此外,我需要范围从 0 开始,而不是特定的起始数字(尽管如果有它会很好)
您可以在新创建的数组的键上使用扩展运算符。
[...Array(n).keys()]
或者
Array.from(Array(n).keys())
该Array.from()
如果与typescript工作语法是必要的
我还发现了一种更直观的使用方法Array.from
:
const range = n => Array.from({length: n}, (value, key) => key)
现在这个range
函数将返回从 0 到 n-1 的所有数字
的范围内的修改版本,以支持start
和end
是:
const range = (start, end) => Array.from({length: (end - start)}, (v, k) => k + start);
编辑 正如@marco6 所建议的,如果它适合您的用例,您可以将其作为静态方法
Array.range = (start, end) => Array.from({length: (end - start)}, (v, k) => k + start);
并将其用作
Array.range(3, 9)
[...Array(N)].map((_, i) => from + i * step);
示例和其他替代方案
[...Array(10)].map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]
Array.from(Array(10)).map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]
Array.from(Array(10).keys()).map(i => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]
[...Array(10).keys()].map(i => 4 + i * -2);
//=> [4, 2, 0, -2, -4, -6, -8, -10, -12, -14]
Array(10).fill(0).map((_, i) => 4 + i * 2);
//=> [4, 6, 8, 10, 12, 14, 16, 18, 20, 22]
Array(10).fill().map((_, i) => 4 + i * -2);
//=> [4, 2, 0, -2, -4, -6, -8, -10, -12, -14]
范围函数
const range = (from, to, step) =>
[...Array(Math.floor((to - from) / step) + 1)].map((_, i) => from + i * step);
range(0, 9, 2);
//=> [0, 2, 4, 6, 8]
// can also assign range function as static method in Array class (but not recommended )
Array.range = (from, to, step) =>
[...Array(Math.floor((to - from) / step) + 1)].map((_, i) => from + i * step);
Array.range(2, 10, 2);
//=> [2, 4, 6, 8, 10]
Array.range(0, 10, 1);
//=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Array.range(2, 10, -1);
//=> []
Array.range(3, 0, -1);
//=> [3, 2, 1, 0]
作为迭代器
class Range {
constructor(total = 0, step = 1, from = 0) {
this[Symbol.iterator] = function* () {
for (let i = 0; i < total; yield from + i++ * step) {}
};
}
}
[...new Range(5)]; // Five Elements
//=> [0, 1, 2, 3, 4]
[...new Range(5, 2)]; // Five Elements With Step 2
//=> [0, 2, 4, 6, 8]
[...new Range(5, -2, 10)]; // Five Elements With Step -2 From 10
//=>[10, 8, 6, 4, 2]
[...new Range(5, -2, -10)]; // Five Elements With Step -2 From -10
//=> [-10, -12, -14, -16, -18]
// Also works with for..of loop
for (i of new Range(5, -2, 10)) console.log(i);
// 10 8 6 4 2
仅作为发电机
const Range = function* (total = 0, step = 1, from = 0) {
for (let i = 0; i < total; yield from + i++ * step) {}
};
Array.from(Range(5, -2, -10));
//=> [-10, -12, -14, -16, -18]
[...Range(5, -2, -10)]; // Five Elements With Step -2 From -10
//=> [-10, -12, -14, -16, -18]
// Also works with for..of loop
for (i of Range(5, -2, 10)) console.log(i);
// 10 8 6 4 2
// Lazy loaded way
const number0toInf = Range(Infinity);
number0toInf.next().value;
//=> 0
number0toInf.next().value;
//=> 1
// ...
class Range2 {
constructor(to = 0, step = 1, from = 0) {
this[Symbol.iterator] = function* () {
let i = 0,
length = Math.floor((to - from) / step) + 1;
while (i < length) yield from + i++ * step;
};
}
}
[...new Range2(5)]; // First 5 Whole Numbers
//=> [0, 1, 2, 3, 4, 5]
[...new Range2(5, 2)]; // From 0 to 5 with step 2
//=> [0, 2, 4]
[...new Range2(5, -2, 10)]; // From 10 to 5 with step -2
//=> [10, 8, 6]
使用发电机
const Range2 = function* (to = 0, step = 1, from = 0) {
let i = 0,
length = Math.floor((to - from) / step) + 1;
while (i < length) yield from + i++ * step;
};
[...Range2(5, -2, 10)]; // From 10 to 5 with step -2
//=> [10, 8, 6]
let even4to10 = Range2(10, 2, 4);
even4to10.next().value;
//=> 4
even4to10.next().value;
//=> 6
even4to10.next().value;
//=> 8
even4to10.next().value;
//=> 10
even4to10.next().value;
//=> undefined
interface _Iterable extends Iterable<{}> {
length: number;
}
class _Array<T> extends Array<T> {
static range(from: number, to: number, step: number): number[] {
return Array.from(
<_Iterable>{ length: Math.floor((to - from) / step) + 1 },
(v, k) => from + k * step
);
}
}
_Array.range(0, 9, 1);
//=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
更新
class _Array<T> extends Array<T> {
static range(from: number, to: number, step: number): number[] {
return [...Array(Math.floor((to - from) / step) + 1)].map(
(v, k) => from + k * step
);
}
}
_Array.range(0, 9, 1);
编辑
class _Array<T> extends Array<T> {
static range(from: number, to: number, step: number): number[] {
return Array.from(Array(Math.floor((to - from) / step) + 1)).map(
(v, k) => from + k * step
);
}
}
_Array.range(0, 9, 1);
对于数字 0 到 5
[...Array(5).keys()];
=> [0, 1, 2, 3, 4]
许多这些解决方案建立在实例化真实的 Array 对象之上,这可以在很多情况下完成工作,但不能支持range(Infinity)
. 您可以使用一个简单的生成器来避免这些问题并支持无限序列:
function* range( start, end, step = 1 ){
if( end === undefined ) [end, start] = [start, 0];
for( let n = start; n < end; n += step ) yield n;
}
例子:
Array.from(range(10)); // [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
Array.from(range(10, 20)); // [ 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 ]
i = range(10, Infinity);
i.next(); // { value: 10, done: false }
i.next(); // { value: 11, done: false }
i.next(); // { value: 12, done: false }
i.next(); // { value: 13, done: false }
i.next(); // { value: 14, done: false }