使用padStart

Question

我实现了一种生成带有可重复计数且前缀为0的项目列表的方法。生成此类列表的最佳方法是什么？

当前行为：

const generateList = (length, n, i) => {
let b = n+i

return b.toString().padStart(length.toString().length + n.toString.length, 0)
}

Array(10).fill(null).map((x, i) => generateList(10,2, i))

输出结果：

["002", "003", "004", "005", "006", "007", "008", "009", "010", "011"]

您是否有其他想法？

Answer 1

您可以确定开始时需要的字符数，并使用预定值来格式化数组的输出。

function createList(startValue, endValue) {
  let 
    // The minimum output length, for a single digit number, is 2 chars.
    outputLength = 2,
    testValue = 10,
    // Create an empty array which has as many items as numbers we need to
    // generate for the output. Add 1 to the end value as this is to be 
    // inclusive of the range to create. If the +1 is not done the resulting 
    // array is 1 item too small.
    emptyArray = Array(endValue - startValue + 1);
    
  // As long as test value is less than the end value, keep increasing the 
  // output size by 1 and continue to the next multiple of 10.
  while (testValue <= endValue) {
    outputLength++;
    testValue = testValue * 10;
  }
  
  // Create a new array, with the same length as the empty array created
  // earlier. For each position place a padded number into the output array.
  return Array.from(emptyArray, (currentValue, index) => {
    // Pad the current value to the determined max length.
    return (startValue + index).toString().padStart(outputLength, '0');
  });
}

function createListWithLength(length, startValue = 0) {
  return createList(startValue, startValue + length);
}

console.log(createList(2,10));
console.log(createListWithLength(30));
console.log(createListWithLength(10, 995));

Answer 2

看看发电机：

function* range(from, to) {
  for (var i=from; i<to; i++)
    yield i;
}
function* paddedRange(from, to) {
  const length = (to-1).toString(10) + 1 /* at least one pad */;
  for (const i of range(from, to))
    yield i.padStart(length, '0');
}

console.log(Array.from(paddedRange(2, 12)));

您也可以将循环从range插入paddedRange，或者可以使其直接返回数组：

function paddedRange(from, to) {
  const length = (to-1).toString(10) + 1 /* at least one pad */;
  return Array.from(range(from, to), i => i.padStart(length, '0'));
}

console.log(paddedRange(2, 12));

主要的简化是，您应该只计算一次填充长度，并为其指定一个命名性名称，而不是针对每个数字再次计算。另外，范围通常由下端和上端给出，而不是由开始和长度给出，但是如果出于某些原因需要后者，则可以轻松切换回去。

Answer 3

不确定，但也许是这样

const generateList = length => Array(length).fill('0').map((item, index) => item + index);

console.log(generateList(20));