Javascript - How To Prevent Tofixed From Rounding Off Decimal Numbers

I'm very new to html, javascript, and css so please forgive if my question sounds idiotic to you. My question is how can I prevent the function toFixed() from rounding of the decim

Solution 1:

That's even simpler:

functiontruncateToDecimals(num, dec = 2) {
  const calcDec = Math.pow(10, dec);
  returnMath.trunc(num * calcDec) / calcDec;
}

So:

truncateToDecimals(123456.786) -> 123456.78

Solution 2:

Round the number (down) to the nearest cent first:

val = Math.floor(100 * val) / 100;

EDIT It's been pointed out that this fails for e.g. 1.13. I should have known better myself!

This fails because the internal floating point representation of 1.13 is very slightly less than 1.13 - multiplying that by 100 doesn't produce 113 but 112.99999999999998578915 and then rounding that down takes it to 1.12

Having re-read the question, it seems that you're really only trying to perform input validation (see below), in which case you should use normal form validation techniques and you shouldn't use .toFixed() at all. That function is for presenting numbers, not calculating with them.

$('#txtAmount').on('keypress', function (e) {
    var k = String.fromCharCode(e.charCode);
    var v = this.value;
    var dp = v.indexOf('.');

    // reject illegal charsif ((k < '0' || k > '9') && k !== '.') returnfalse;

    // reject any input that takes the length// two or more beyond the decimal pointif (dp >= 0 && v.length > dp + 2) {
        returnfalse;
    }

    // don't accept >1 decimal point, or as first charif (k === '.' && (dp >= 0 || v.length === 0)) {
        returnfalse;
    }
});

Solution 3:

you can give this a try, it won't round your decimals

/**
 * @param {any} input 
 * @param {number} decimals 
 */var toFixed = function(input, decimals) {
  var arr = ("" + input).split(".");
  if (arr.length === 1) return input;
  varint = arr[0],
      max = arr[1].length,
      dec = arr[1].substr(0, decimals > max ? max : decimals);
  return decimals === 0 ? int : [int, "." , dec].join("");
}

Solution 4:

Additionally, to prevent toFixed() from rounding off decimal numbers and to make your number into two decimal places you can use this,

val = (Math.floor(100 * val) / 100).toFixed(2);

Solution 5:

if you want to avoid rounding off... Ex. 1.669 => 1.67, 548.466 => 548.47

The function result looks like: 1.669 => 1.66, 548.466 => 548.46

Then the following JQuery function will help you. It is tested and working properly.

<input name="a" type="text" id="a" size="7%" tabindex="2">




  $('#a').keyup(function(e){
        if($(this).val().indexOf('.')!=-1){ 
            if($(this).val()=="." && $(this).val().length==1){
                this.value = parseFloat(0).toFixed(1);
            }elseif($(this).val().split(".")[1].length > 2){                
                if( isNaN( parseFloat( this.value ) ) ) 
                    return;
                  this.value = $(this).val().split(".")[0]+"."+$(this).val().split(".")[1].substring(0,2);
            }   
        }
   });