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For adding commas, if you're using javascript, you can simply use:

number.toLocaleString()

and it will return the number formatted for whatever the user's language prefers, eg. comma separation for US locale, period separation for many European locales, etc. You can pass a string to the function to specify the locale if you want to be opinionated, such as 'en-US' for US locales.

If you want to do scientific notation you could do:

number.toExponential()

If you want to use your own abbreviations, you could do something like:

const num = 1234567890;
const commaNum = number.toLocaleString('en-US'); // Returns 1,234,567,890 regardless of user's locale
const splitNum = commaNum.split(','); // Splits the string into an array of strings using the commas as the split points
const displayNum = splitNum[0]; // Set the display num to the most significant digits; 1 in this case
if (splitNum.length === 1) {
    return displayNum // No commas means no abbreviation necessary
}
else
if (splitNum.length === 2) {
    return displayNum + "K"; // 1 comma means we're dealling with thousands
}
else
if (splitNum.length === 3) {
    return displayNum + "M"; // 2 commas means we're dealling with millions
}
else
if (splitNum.length === 4) {
    return displayNum + "B"; // 3 commas means we're dealling with billions; which we are in this specific case
}
else
if (splitNum.length === 5) {
    // Continue the pattern until numbers get so large that scientific notation is the only thing that's reasonable any more...
}

The above code will only return 1-3 whole number digits followed by an abbreviation letter.