How to get typeof entered value?

Question

UPDATE: [SOLVED] Thanks everyone for answering me, I have tried two method and it is really work! Here are jsbin for them:

This one was inspired by Secret's answer

This one is from Alexander's O Mara's answer

I'm trying to check if the entered value is number or not. I'm using typeof to check it. If entered value is number, alert('number');. But if entered value is string, alert(’string');.

The problem is, it always alert(’string'); although the entered value is number.

What's wrong? How can I solve it?

Here is my code:

<input type="text" placeholder="inputText" id="inputText">
<input type="button" onclick="alertType()" value="alertType">
<script>
 function alertType()
 {
  var someStr = document.getElementById("inputText").value;
  var someStrType = typeof someStr;
  alert(someStrType);
 }
</script>

See [Validate decimal numbers in JavaScript - IsNumeric()](https://stackoverflow.com/questions/18082/validate-decimal-numbers-in-javascript-isnumeric) — Chris, Feb 28 '15 at 05:52
Define "number" Do you mean an integer? A decimal? Can it be negative? — aquinas, Feb 28 '15 at 05:55
possible duplicate of [Get the type of a input from an HTML form](http://stackoverflow.com/questions/19513041/get-the-type-of-a-input-from-an-html-form) — Gildas.Tambo, Feb 28 '15 at 05:59

score 2 · Accepted Answer · answered Feb 28 '15 at 05:53

You could simply cast the string to a number using Number, and use isNaN to check if it was successfully cast to a number. Number will return NaN if it fails to cast to a number, which isNaN can detect.

<input type="text" placeholder="inputText" id="inputText">
<input type="button" onclick="alertType()" value="alertType">
<script>
 function alertType()
 {
  var someStr = document.getElementById("inputText").value;
  var someNum = Number(someStr);
  if (isNaN(someNum)) {
    alert('not a number');
  }
  else {
    alert('a number');
  }
 }
</script>

Thanks! Use `Number()` as a magical spell to cast it to number really work! — Anakin, Feb 28 '15 at 06:00

score 1 · Answer 2 · answered Feb 28 '15 at 06:01

1

Problem here is your data source is textbox which gives value as string. You need to parse it to number.

answered Feb 28 '15 at 06:01

score 1 · Answer 3 · answered Feb 28 '15 at 06:02

var my_numberA = 3;     //  This is typeof number
var my_numberB = '3';   //  This is typeof string

So depending on how you write it: a 3 is a number where '3' is a string

The trick is to do the following:

Any string multiplied by 1 will convert the string to a number. However, multiplying a string that can not be represented by a number will return an error. So you need to compensate for that possibility with a try{}catch(err){} that converts the string to a number if possible

function convertToNumber(input){
    try{var output = 1*input}catch(error){var output = input}
    return output
}

var my_numberA = 3;     //  This is typeof number
var my_numberB = '3';   //  This is typeof string

console.log( typeof my_numberA ) // Will show 'number'
console.log( typeof my_numberB ) // Will show 'string'

console.log( typeof convertToNumber(my_numberA) ) // Will show 'number'
console.log( typeof convertToNumber(my_numberB) ) // Will show 'number'

I prefer this in some cases rather than the Number() function because it returns the same passed object instead of returning NaN.

score 0 · Answer 4 · answered Feb 28 '15 at 05:46

0

The thing is, when you get the inputText value from your dom, it is a string. For example, "12" is a string, vs. a 12

What you can do is to check if it is not a number:

function alertType()
 {
  var someStr = document.getElementById("inputText").value;
  if(isNaN(someStr)){
     //it's not a number!
  } else  { 
     //it's a number!
  }
 }

answered Feb 28 '15 at 05:46

Secret

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Be careful though, isNaN returns `false` for things like `0xdeadbeef`, an empty string, etc. Depending on what you want, a regex is often a better choice... – aquinas Feb 28 '15 at 05:53

score 0 · Answer 5 · answered Feb 28 '15 at 06:00

Try this ...

$('#clickMe').click(function () {
    var inputVal = $("#inputText").val();
    var value = Number(inputVal);

    if (isNaN(value)) {
        alert('not a number');
    } else {
        alert('a number');
    }
});

https://jsfiddle.net/mky9vxdy/1/

How to get typeof entered value?

5 Answers5