我正在寻找以下方法的任何替代方法,以创建包含1到N的JavaScript数组,其中N仅在运行时已知。

var foo = [];

for (var i = 1; i <= N; i++) {
   foo.push(i);
}

对我来说,我觉得应该有一种不用循环的方法。


当前回答

这可能是生成数字数组的最快方法

最短的

var a=[],b=N;while(b--)a[b]=b+1;

内联

var arr=(function(a,b){while(a--)b[a]=a;return b})(10,[]);
//arr=[0,1,2,3,4,5,6,7,8,9]

如果您想从1开始

var arr=(function(a,b){while(a--)b[a]=a+1;return b})(10,[]);
//arr=[1,2,3,4,5,6,7,8,9,10]

想要功能吗?

function range(a,b,c){c=[];while(a--)c[a]=a+b;return c}; //length,start,placeholder
var arr=range(10,5);
//arr=[5,6,7,8,9,10,11,12,13,14]

WHY?

while是最快的循环直接设置比推送更快[]比新阵列(10)更快它很短。。。查看第一个代码。然后看看这里的所有其他函数。

如果你喜欢,就不能没有

for(var a=[],b=7;b>0;a[--b]=b+1); //a=[1,2,3,4,5,6,7]

or

for(var a=[],b=7;b--;a[b]=b+1); //a=[1,2,3,4,5,6,7]

其他回答

可以使用Int8Array、Int16Array和Int32Array创建范围从1到n的数组,如下所示:

const zeroTo100 = new Int8Array(100).map((curr, index) => curr = index + 1);
/* Int8Array(100) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 
36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 
55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 
74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 
93, 94, 95, 96, 97, 98, 99, 100]

还可以使用以下类型化数组在数组中生成1到n个项。

Uint8Array、Uint16Array和Uint32ArrayBigInt64阵列Uint8约束阵列浮置阵列32、浮置阵列64

当然,除了数字之外,您无法在这些数组中放置任何东西,所以使用这个小快捷方式会带来风险。

此外,如果您只需要一个包含n个零的数组,那么只需执行以下操作:

const arr_100_0s = new Int8Array(100)

编辑:您可以使用它快速生成范围,如下所示:

function range(start, end) {
    const arr = new Int8Array(end - start + 1).map((curr, i) => curr + i + start);
    return arr;
}

range(15, 30); // Int8Array(16) [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]

不完全符合用户的要求,但与IMO高度相关。

试试看:

var foo = [1, 2, 3, 4, 5];

如果您正在使用CoffeeScript,可以通过执行以下操作创建范围:

var foo = [1..5]; 

否则,如果您使用的是普通JavaScript,那么如果要将数组初始化为可变长度,则必须使用循环。

在ES6中,您可以执行以下操作:

数组(N).fill().map((e,i)=>i+1);

http://jsbin.com/molabiluwa/edit?js安慰

编辑:更新问题后,将数组(45)更改为数组(N)。

控制台日志(数组(45).填充(0).映射((e,i)=>i+1));

非常简单,容易生成精确的1-N

const[,…result]=数组(11).keys();console.log('结果:',结果);

以下是摘要(在控制台中运行):

// setup:
var n = 10000000;
function* rangeIter(a, b) {
    for (let i = a; i <= b; ++i) yield i;
}
function range(n) { 
    let a = []
    for (; n--; a[n] = n);
    return a;
}
function sequence(max, step = 1) {
    return {
        [Symbol.iterator]: function* () {
            for (let i = 1; i <= max; i += step) yield i
        }
    }
}

var t0, t1, arr;
// tests
t0 = performance.now();
arr = Array.from({ length: n }, (a, i) => 1)
t1 = performance.now();
console.log("Array.from({ length: n }, (a, i) => 1) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = range(n);
t1 = performance.now();
console.log("range(n) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = Array.from(rangeIter(0, n));
t1 = performance.now();
console.log("Array.from(rangeIter(0, n)) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = [...rangeIter(0, n)];
t1 = performance.now();
console.log("[...rangeIter(0, n)] Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = Array.from(sequence(n));
t1 = performance.now();
console.log("Array.from(sequence(n)) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = [...sequence(n)];
t1 = performance.now();
console.log("[...sequence(n)] Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = Array(n).fill(0).map(Number.call, Number);
t1 = performance.now();
console.log("Array(n).fill(0).map(Number.call, Number) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = Array.from(Array(n).keys());
t1 = performance.now();
console.log("Array.from(Array(n).keys()) Took " + (t1 - t0) + " milliseconds.");

t0 = performance.now();
arr = [...Array(n).keys()];
t1 = performance.now();
console.log("[...Array(n).keys()] Took " + (t1 - t0) + " milliseconds.");

最快的是Array(n).fill(0).map(Number.call,Number),第二个是[…Array(n).keys()]

但是。。。rangeIter的方式非常方便(可以内联),速度快,功能更强大