Javascript parsing an integer from a string

What I want to do is determine if a string is numeric. I would like to know what people think about the two solutions I am trying to decide between (OR if there is a better solution that I have not found yet). The parseInt function is not suitable because it will return an integer value for a parameter like "40 years old". The two solutions I am deciding between are:

Use Integer.valueOf开发者_如何学Python() with try catch

function isNumeric(quantity)
{
    var isNumeric = true
    try
    {
        Integer.valueOf(quantity)
    }
    catch(err)
    {
        isNumeric = false
    }
    return isNumeric
}

Or check each character individually

function IsNumeric(quantity)
{
    var validChars = "0123456789";
    var isNumber = true;
    var nextChar;

    for (i = 0; i < quantity.length && isNumber == true; i++) 
    { 
        nexChar = quantity.charAt(i); 
        if (validChars.indexOf(nextChar) == -1) 
        {
            isNumber = false;
        }
    }
    return IsNumber;
}

I would have thought there would be a simpler solution than both of these though. Have I just missed something?

NOTE: I am using jQuery aswel so if there is a jQuery solution that that would be sufficient

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I had to do something like you want, but I needed to verify if a variable contained a number without knowing its type, it could be a numeric string (considering also exponential notation, etc.), a Number object, basically anything.

And I had to take care about implicit type conversion, for example !isNaN(true) == true was not good.

I ended up writing a set of 30+ unit test that you can find here, and I use the following function, that passes all my tests:

function isNumber(n) {
  return !isNaN(parseFloat(n)) && isFinite(n);
}

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Why not isNaN(obj)?

function IsNumeric (value) {
    return (!((isNaN(value)) || (value.length == 0)));
}

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how about a regex?

function IsNumeric(string) { 
    return string.match(/^\d+$/) !== null;
}

(not tested or very defensive, but you get the point)

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If you are only testing strings, why not let any string use the method?

String.prototype.isNumeric= function(){
 return parseFloat(this)== this;
}

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This would work for most values

function isNumericString(s)
{
   return !!s && !isNaN(+s);
}

generally unary + is the best way to convert to number. no base issue, no dangling non digit problem.

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I suppose you could use a regular expression to validate the input, but I honestly don't see what's wrong with the first one.

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Here is my solution with parseInt that will work:

var str = "40 years old";
var isNumeric = parseInt(str) == str ? true : false;