typeof() function errors in javascript

Question

Possible Duplicate:
Is there a (built-in) way in JavaScript to check if a string is a valid number?

I have an input search bar in HTML

<form class="form-inline" action="javascript:displayResult()">          
    <input id="searchKey" >
    <button onclick="result()" type="button" class="btn btn-warning btn ">
          Go
    </button>                   
</form>

This is the Javascript function

function result() {     
    search($('#searchKey').val());    

    if(typeof(searchKey)=="number") { // checking if this is a number
       someFunction();
    }
};

The problem is , for each entry to the search bar I get the value as a string , even if it is "hello" or 9789 in the search bar . I used alert(typeof(searchKey)); to verify and it always return the type as string

I am trying to differentiate between a number and a string at the search bar , I am sure there is a better way to do this , but I am unsure about why this is not working

I cannot use parseInt() as I need to differentiate between text and number dynamically

When would code after a `return` statement get executed? – DCoder Aug 04 '12 at 08:26 — DCoder, Aug 04 '12 at 08:26
You are calling it after return man! – AdityaParab Aug 04 '12 at 08:27 — AdityaParab, Aug 04 '12 at 08:27
apologies , I ave edited my code – alex Aug 04 '12 at 08:27 — alex, Aug 04 '12 at 08:27
is `searchKey` a global variable? – Ilmo Euro Aug 04 '12 at 08:27 — Ilmo Euro, Aug 04 '12 at 08:27
try parseInt(str, base) if it fails it should just return 0 – Zaffy Aug 04 '12 at 08:37 — Zaffy, Aug 04 '12 at 08:37

Zeta · Accepted Answer · 2012-08-04T10:48:32.753

The value of a <input type="text"> is always a string. You can, however, parse it as an number by using parseInt. It will result in NaN if not number could be parsed from the string. Don't forget you'll have to use isNaN for this, as myNumber === NaN isn't a valid operation.

Even better, use isNaN(+searchKey), as the unary operand will call ToNumber. However, this will ignore whitespace.

9.3.1 ToNumber Applied to the String Type

ToNumber applied to Strings applies the following grammar to the input String. If the grammar cannot interpret the String as an expansion of StringNumericLiteral, then the result of ToNumber is NaN.

[see http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf for the actual rules]

11.4.6 Unary + Operator

The unary + operator converts its operand to Number type. The production UnaryExpression : + UnaryExpression is evaluated as follows:

Let expr be the result of evaluating UnaryExpression.

Return ToNumber(GetValue(expr)).

@blueiur: You could either use `parseInt(val).toString() == val` to make sure that both values are the same or use a [regular expression](http://stackoverflow.com/a/11807113/1139697). — Zeta, Aug 04 '12 at 08:32

score 3 · Answer 2 · answered Aug 04 '12 at 08:27

3

A text input field always contains a string value. Try if (!isNaN(searchKey)) to test for numeric value. Alternatively you could use a Regular Expression: /^\d+$/.test(searchKey)

answered Aug 04 '12 at 08:27

KooiInc

119,216
31
141
177

score 3 · Answer 3 · answered Aug 04 '12 at 08:27

3

use

if(!isNaN(searchKey))

instead of

if(typeof(searchKey)=="number")

answered Aug 04 '12 at 08:27

Mithun Satheesh

27,240
14
77
101

typeof() function errors in javascript

3 Answers3

9.3.1 ToNumber Applied to the String Type

11.4.6 Unary + Operator