round a number to the nearest ten thousandth in javascript

You can use the built-in Math.round() function to round a number to the nearest ten thousandth in JavaScript. Here's an example function that does this:

index.tsx
function roundToTenThousandth(num) {
  return Math.round(num * 10000) / 10000;
}
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Here, we multiply the input number by 10000 to shift the decimal point four places to the right, so that the digit we want to round to is in the ones place. Then we use Math.round() to round the number to the nearest integer. Finally, we divide by 10000 to shift the decimal point back four places to the left, so that we get the rounded number with four decimal places.

For example:

index.tsx
roundToTenThousandth(1234.56789); // returns 1234.5679
roundToTenThousandth(9876.54321); // returns 9876.5432
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Note that this function doesn't limit the number of decimal places in the input number, so if you need to limit it to four decimal places before rounding, you can use num.toFixed(4) to do so:

index.tsx
function roundToTenThousandth(num) {
  return Math.round(num.toFixed(4) * 10000) / 10000;
}
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This will ensure that the input number is rounded to the nearest ten thousandth with at most four decimal places.