允许html输入框仅输入一个完整的数字，并精确输入十进制.5

Question

I'm making web application that requires users to enter number with one decimal place. I restrict users from entering other characters that numbers from using this javascript code

html

<input type="number" name='days' class="w3-input w3-padding-tiny" id="cntday"  onkeypress="return isNumberKey(event)" placeholder="Enter days"/>

javascript

function isNumberKey(evt) {
          var charCode = (evt.which) ? evt.which : evt.keyCode;
          if (charCode != 46 && charCode > 31 &&
             (charCode < 48 || charCode > 57))
             return false;
          return true;
         }  

but this function only prevent users from entering characters other than numbers. I need to prevent users from entering more than one decimal places as well as entered decimal should be .5

it's like this

• if user enter 5.55 it should replace with 5.5 OR prevent user to input additional decimal

• and if user enter 5.2 OR any decimal it should be replace with 5.5 in other words users should only able to enter number with decimal .5

how can I achieve this with my current onkeypress function ?

This is NOT a duplicate of the other question. Stop flagging this

Answer 1

You can do it by split the number into two parts:

Part 1 for natural number.

Part 2 for decimal number.

then you can replace any entered decimal number to .5

Something like this:

 $('input').keyup(function() { var value = this.value; var pos = value.indexOf("."); var result; if (pos !== -1) { var part1 = value.substr(0, pos); var part2 = value.substr(pos); result = part1 + part2.replace(part2,".5") $('input').val(result); } }); function isNumberKey(evt) { var charCode = (evt.which) ? evt.which : evt.keyCode; if (charCode != 46 && charCode > 31 && (charCode < 48 || charCode > 57)) return false; return true; } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <input type="number" name='days' class="w3-input w3-padding-tiny" id="cntday" onkeypress="return isNumberKey(event)" placeholder="Enter days"/> 

Answer 2

Use this

$('#cntday').keyup(function() {
    if(this.value %1 != 0.5){
        this.value = this.value - this.value%1 + 0.5;
    }
});

The condition checks whether a decimal has been entered or not and as soon as a decimal is entered and a number is entered it changes it to .5 It fulfills both the requirements you mentioned. Check it here https://jsfiddle.net/xn0koawx/