JavaScript数学，以.05为增量舍入到两位小数

Question

I apologise in advance. I've read thru a number of post and I'm sure the answer lies in implementing the toFixed() method, but can't work out how.

$('.addsurcharge').click(function() {               
    $('span.depositamount').text(function(i,v) {
        return Math.round(parseInt(v * 100, 10) * 0.025) / 100 + (v * 1);
    });      
});

$('.nosurcharge').click(function() {            
    $('span.depositamount').text(function(i,v) {
        return Math.round(parseInt(v * 100, 10) * -0.025) / 100 + (v * 1);
    });      
});

Basically, the above is adding (or subtracting) a 2.5% surcharge for AMEX deposits and I want it to round up to the nearest two decimal amount. Preferably in .05 increments.

Help appreciated!

Answer 1

Although the post is a bit old, the question isn't. I think what the poster meant was, that some currency calculate with cents, but the prices are given in x.00 or x.05 cents. For example Swiss currency.

The solution, borrowed from RobG's answer with a little fix:

function roundToFiveCents(v) {
    var len;
    // Format to 2 numbers after decimal point an turn dollars into cents
    v = v.toFixed(2) * 100;

    // Get residual cents
    var r = v % 5;

    // Round to 5c
    if (r) {
        v -= (r === 1 || r === 2) ? r : r - 5;
    }

    // Convert to string
    v = v + '';
    len = v.length - 2;

    // Return formatted string
    return v.substring(0, len) + '.' + v.substring(len);
}

Answer 2

If your question is "How do I take v , a variable that contains a dollar-and-cents amount, and apply a 2.5% AMEX surcharge with the result rounded to the nearest cent (ie, to two decimals)?" Then you can try this:

return (v * 1.025).toFixed(2);

If you have a variable surcharge try this:

var surcharge = 0.025; // or whatever percentage applies

return (v * (1 + surchage)).toFixed(2);

Note that toFixed returns a string representation, but it does the rounding for you.

(Regarding your "nosurcharge" function, you can't remove a 0.025 surcharge that was applied previously by multiplying by -0.025. You apply the surchage by multiplying by 1.025, so you remove it by dividing by 1.025.)

Answer 3

The easiest way for currency is to work in the minor units, then round and convert to major units only at the end. So for a system with dollars and cents, work in cents until the end, then convert to dollars. If the text to be input is of the format "2.03", then it can rounded it to the nearest $0.05 using something like:

function roundToFiveCents(v) {

  // Turn dollars into cents and convert to number
  var len;
  v = v * 100;

  // Get residual cents
  var r = v % 5;

  // Round to 5c
  if (r) {
    v -= (r == 1 || r == 2)? r : r-5;
  }

  // Convert to string
  v = v + '';
  len = v.length - 2;

  // Return formatted string
  return v.substring(0, len) + '.' + v.substring(len);
}

That can be more concise, but I can't see the point, it would only server to obfuscate. String manipulation is very fast and replaces the uncertainty of javascript multiplication and division of decimal fractions with simple addition and subtraction.

eg borrowing from rfausak's answer:

// Returns string, remove ' + ''' to return number
function roundToFiveCents(v) {
  return (Math.round(v*20)/20).toFixed(2) + '';
}

Answer 4

var n = 8.22354;
roundx(n, 3)

function roundx(num, decPlace) {
  return Math.round(num * Math.pow(10, decPlace))/Math.pow(10, decPlace);
}

This simple function works well for rounding to x number of places.

Answer 5

How about the following javascript:

function my_round(x) {
    x *= 20;
    x = Math.ceil(x);
    return x / 20;
}
var amount = 3.37;
alert(my_round(amount));