Question

How to replace a digit in a floating-point number by index with JavaScript

Answer 1

function replaceFloatDigit(number, position, newDigit) {
    // Validate that newDigit is indeed a single digit
    if (newDigit < '0' || newDigit > '9') {
        throw new Error("Replacement must be a digit (0-9).");
    }

    // Convert number to string with fixed precision (10 decimal places)
    let strNum = number.toFixed(10);

    // Validate position
    if (position < 0 || position >= strNum.length) {
        throw new Error("Position is out of range for the number string.");
    }

    // Ensure position points to a digit
    if (strNum[position] === '.' || strNum[position] === '-') {
        throw new Error("Position points to a non-digit character.");
    }

    // Replace digit
    strNum = strNum.substring(0, position) + newDigit + strNum.substring(position + 1);

    // Convert back to float
    return parseFloat(strNum);
}

try {
    const num = 89710.291;
    const pos = 2;          // 0-based index
    const newDigit = '8';

    const result = replaceFloatDigit(num, pos, newDigit);
    console.log(`Modified number: ${result.toFixed(3)}`);
} catch (e) {
    console.error("Error: " + e.message);
}



/*
run:
  
Modified number: 89810.291
  
*/

 

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