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。
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
不支持在ES6解决方案中创建阵列
js不适用于100阵列
1.焊盘启动
// string arr
const arr = [...``.padStart(100, ` `)].map((item, i) => i + 1 + ``);
// (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"]
// number arr
const arr = [...``.padStart(100, ` `)].map((item, i) => i + 1);
// (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]
2.类型化阵列
Uint8阵列
// number arr
const arr = new Uint8Array(100).map((item, i) => i + 1);
// Uint8Array(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]
// string arr
const arr = [...new Uint8Array(100).map((item, i) => i + 1)].map((item, i) => i + 1 + ``);
// (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"]
其他回答
使用ES6,您可以做到:
// `n` is the size you want to initialize your array
// `null` is what the array will be filled with (can be any other value)
Array(n).fill(null)
如果我得到了你想要的,你需要一个数字数组1..n,以后可以循环使用。
如果这就是你所需要的,你能代替它吗?
var foo = new Array(45); // create an empty array with length 45
然后当你想使用它时…(例如,未优化)
for(var i = 0; i < foo.length; i++){
document.write('Item: ' + (i + 1) + ' of ' + foo.length + '<br/>');
}
例如,如果你不需要在数组中存储任何东西,你只需要一个长度合适的容器,你可以遍历它。。。这可能更容易。
请在此处查看实际操作:http://jsfiddle.net/3kcvm/
比字符串变体简单一点:
// create range by N
Array(N).join(0).split(0);
// create a range starting with 0 as the value
Array(7).join(0).split(0).map((v, i) => i + 1) // [1, 2, 3, 4, 5, 6, 7]
更新(2018年1月4日):更新以解决确切的OP问题。感谢@lessless发出此消息!
使用ES6
const generateArray = n => [...Array(n)].map((_, index) => index + 1);
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