CODEWITHSUNDEEP
javascript
MariaL
MariaL

Reputation: 1242

get input value with math function in variable

I've got some javascript to change the input value via plus/minus buttons. I now need to save the value after the value has been decremented in a variable and output it as a number.

The javascript for the decrement looks something like this:

if (!isNaN(currentVal) && currentVal > 0) {
    // Decrement one
    $('input[id='+fieldName+']').val(currentVal - 1);
    var test = parseInt($('input[id='+fieldName+']').val(currentVal - 1).val());
    alert(test);
}

So as you can see I'm trying to get the updated value of the input in a variable called 'test', but all I'm getting is a NaN. Any ideas how to output the updated value of the input as a number within my test variable?

Upvotes: 0

Views: 171

Answers (3)

r0ulito
r0ulito

Reputation: 487

Something showed up to me.

You are using jquery (I think it's right cause of the $ selector), and you are getting the ID with bracket notation. Why not using something like

var selector = '#' + fieldName;

Then

$(selector)???

Another thing, usually when I'm trying something with javascript, I try it into the developer tool's console of my browser. Doing it step by step avoid mistakes

Upvotes: 0

Miroslav Glamuzina
Miroslav Glamuzina

Reputation: 4557

You can use double Tilda operator ~~ which behaves like Math.floor() except will return you 0 if the value is not a number.

I believe this is the solution you are looking for:

let inputField = document.querySelector('input[name="fieldName"]');


increment = () => {
  let currentValue = ~~inputField.value;
  alert(currentValue);
  inputField.value = currentValue + 1;
};

decrement = () => {
  let currentValue = ~~inputField.value;
  alert(currentValue);
  if (currentValue > 0) {
    inputField.value = currentValue - 1;
  }
};
<input type="number" name="fieldName" value="0" />
<button onclick="increment()">+</button>
<button onclick="decrement()">-</button>

Hope this helps,

Upvotes: 0

ABC
ABC

Reputation: 2148

As @trincot said we cannot re-produce your situation. But the reason a NaN would be returned is because.

parseInt Returns an integer number parsed from the given string. If the first character cannot be converted to a number, NaN is returned.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt

let a = '1'
let b = 'Two'

console.log(parseInt(a));
// 1
console.log(parseInt(b));
// NaN
console.log(parseInt(undefined))
// NaN

Upvotes: 1

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