为什么该方法将 padEnd 返回为未定义？

Question

Using the following method, when I am entering 7.0 I get the following error:

Unhandled Rejection (TypeError): Cannot read property 'padEnd' of undefined

formatInput = (value) => {
  const numsAfterDot = 6;
  const isNegative = value < 0;
  const hasDecimals = value.includes(".");
  let absolute = Math.abs(value).toString();
  if (isNaN(absolute)) return;
  else {
    const split = absolute.split(".");
    let start = hasDecimals ? split[0] : absolute.slice(0, 2);
    let rest = hasDecimals ? split[1] : absolute.slice(2, numsAfterDot)
    start = start.padStart(2, "0");
    rest = rest.padEnd(numsAfterDot, "0");
    const result = `${start}.${rest}`;
    return isNegative ? `-${result}` : result;
  }
};

Can someone please help me solve this?

Expected output:

"7.0" should converts to "07.000000"
"12" should converts to "12.000000"
".12" should converts to "00.120000"
"-123" should converts to "-12.300000"
"123456" should converts to "12.345600"

Answer 1

You get the error because you test to see if the string you send in has a decimal point.

const hasDecimals = value.includes(".");

You then convert it to absolute.

let absolute = Math.abs(value).toString();

When you do that it no longer has a decimal point, so the split is going to be ['7']

so there is no split[1] , hence why it is undefined.

Your code is a bit complicated. I would just split, if it is not a length of 2, I would split the string up into two parts and then pad it.

 function custPad (str) { // convert to number const num = +str; // check if negative const neg = num < 0? '-': ''; // get rid of negative, split it at decimal const parts = Math.abs(num).toString().split('.'); // if no decimal, than break it up if (parts.length === 1) { const nums = parts[0]; // grab first two numbers parts[0] = nums.substr(0,2); // grab remaining parts[1] = nums.substr(2, 6); } // build the new string with the padding return neg + parts[0].padStart(2, '0') + "." + parts[1].padEnd(6, '0').substr(0,6); } console.log("7.0", custPad("7.0")) console.log("7", custPad("7")) console.log("0.12", custPad("0.12")); console.log("123", custPad("123")); console.log("-12", custPad("-12")); console.log("123456", custPad("123456")); console.log("12345678911111111", custPad("12345678911111111"));