Javascript Math.floor issue between specific range of numbers

Question

I'm facing an issue with Math.floor function of javascript for the below scenario:

1) from the value betwwen 8192 and 10484,

    if I type 8192.8  -> The Math.floor converts it into 8192.79

    if I type 8192.88  -> The Math.floor converts it into 8192.87

    if I type 8192.3  -> The Math.floor converts it into 8192.29

Strange part is that except from the range given above the function works fine.

HTML:
<div data-bind="text: popIncrease"></div>
<input type="text" data-bind="value: userInput,  valueUpdate: 'afterkeydown'" />

Javascript:

var ViewModel = function () {
var _self = this;
_self.userInput = ko.observable();
_self.popIncrease = ko.computed(function () {

        return parseFloat((Math.floor(_self.userInput() * 100) / 100)).toFixed(2);
});
};

ko.applyBindings(new ViewModel());

jsfiddle:https://jsfiddle.net/91z5bdy4/1/

When I changed 100 with 1000 it solved the error but I do not understand why this happened on the first place?

Answer 1

You can just switch to this:

return parseFloat(_self.userInput()).toFixed(2);

Working version of your jsFiddle: https://jsfiddle.net/jfriend00/5rLL04Lk/

---

Or, if you want to work around some of the idiosyncrasies of .toFixed(), you can use this:

return (Math.round(_self.userInput() * 100) / 100).toFixed(2);

Working jsFiddle: https://jsfiddle.net/jfriend00/xx2aj2L0/

This solution passes all three of your test cases.