how to check whether a var is string or number using javascript

Question

I have a variable var number="1234", though the number is a numeric value but it is between "" so when I check it using typeof or by NaN I got it as a string .

function test()
{
 var number="1234"
if(typeof(number)=="string")
{
 alert("string");
}
if(typeof(number)=="number")
{
 alert("number");
}
}

I got always alert("string"), can you please tell me how can I check if this is a number?

• Gaurav Shah: since you are storing it with "" it will be string only. you need to give var number = 12345
• ipr101: Have a look at the functions defined in this answer - stackoverflow.com/questions/18082/…

Answer 1

As far I understand your question you are asking for a test to detect if a string represents a numeric value.

A quick test should be

function test() {
 var number="1234"
 return (number==Number(number))?"number":"string"
}

As Number, if called without the new keyword convert the string into a number. If the variable content is untouched (== will cast back the numeric value to a string) you are dealing with a number. It is a string otherwise.

function isNumeric(value) {
 return (value==Number(value))?"number":"string"
}
/* tests evaluating true */
console.log(isNumeric("1234")); //integer
console.log(isNumeric("1.234")); // float
console.log(isNumeric("12.34e+1")); // scientific notation
console.log(isNumeric(12)); // Integer
console.log(isNumeric(12.7)); // Float
console.log(isNumeric("0x12")); // hex number
/* tests evaluating false */
console.log(isNumeric("1234e"));
console.log(isNumeric("1,234"));
console.log(isNumeric("12.34b+1"));
console.log(isNumeric("x"));

• RobG: Fails where value is empty string or whitespace as both convert to 0 and 0 == ''.

Answer 2

The line

 var number = "1234";

creates a new String object with the value "1234". By putting the value in quotes, you are saying that it a string.

If you want to check if a string only contains numeric digits, you can use regular expressions.

if (number.match(/^-?\d+$/)) {
 alert("It's a whole number!");
} else if (number.match(/^-?\d+*\.\d+$/)) {
 alert("It's a decimal number!");
}

The pattern /^\d+$/ means: at the start (^) of the string, there is an optional minus sign (-?), then a digit (\d), followed by any more digits (+), and then the end of the string ($). The other pattern just looks for a point between the groups of digits.

• RobG: That will work provided the value is only digits, any other value (such as -1 or 1.5) will return false. A robust isNumber() function has been posted in response to Validate numbers in JavaScript - IsNumeric().

Answer 3

See parseInt and parseFloat

• Romi: using parseInt , it converts both "abcd" and "1234" to a integer. which gives me wrong result. i want only "1234" to be converted into inumeric value
• spender: @Romi, actually the "numeric" value of 'romi' is NaN (not a number). Perhaps you should check if the resultant variable isNaN (developer.mozilla.org/en/JavaScript/Reference/Global_Objects/…)

Answer 4

Convert it to a number then compare it to the original string.

if ( parseFloat(the_string,10) == the_string ) {
 // It is a string containing a number (and only a number)
}

Answer 5

because var number="1234" is a string. the double quotes makes it a literal.

if you want a number use it like this

var number = 1234;

Update:

If you are taking the input from a input tag forexample, the dataType will be string, if you want to convert it to a number, you can use the parseInt() function

var number = "1234";
var newNumber = parseInt(number);
alert(typeof newNumber); // will result in string

• Romi: Ibu: Ya absolutely, but what my problem is i ma getting through it a text box from where i am getting "1234" how can i remove "" to make it a number. although when i put alert on the data i got from text box i get it as 1234 but while checking it gives me a string
• Ibu: See my update @Romi, using parseInt() for integers or parseFloat() for decimal numbers will help fix this problem
• RobG: Fails where the input has trailing non-number characters.

Answer 6

Another easy way:

var num_value = +value;
if(value !== '' && !isNaN(num_value)) {
 // the string contains (is) a number
}

• RobG: empty string converts to zero, so !isNaN(+('')) gives false. Also whitespace and null convert to zero too, so they will return true (though in this case null is not an expected value).
• RobG: I think the simplest is: function isNumber(n) { return !isNaN(parseFloat(n)) && isFinite(n); } posted here.