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Asked 4 days ago. Active 4 days ago. Viewed 23 times. Just plain javascript. Ilyich Ilyich 1, 1 1 gold badge 14 14 silver badges 14 14 bronze badges. Please add your attempt and describe what problems you have with it.

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javascript check if string is number

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The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm hoping there's something in the same conceptual space as the old VB6 IsNumeric function? Of course, you can negate this if you need to.

For example, to implement the IsNumeric example you gave:. Only works if the string only contains numeric characters, else it returns NaN. Empty strings may be a little counter-intuitive. If you're just trying to check if a string is a whole number no decimal placesregex is a good way to go. Other methods such as isNaN are too complicated for something so simple. Note that! The problem with parseFloat is that it will return a number if the string contains any number, even if the string doesn't contain only and exactly a number:.

The problem with Number is that it will return a number in cases where the passed value is not a number at all! The problem with rolling your own regex is that unless you create the exact regex for matching a floating point number as Javascript recognizes it you are going to miss cases or recognize cases where you shouldn't. And even if you can roll your own regex, why? There are simpler built-in ways to do it. However, it turns out that Number and isNaN does the right thing for every case where parseFloat returns a number when it shouldn't, and vice versa.

So to find out if a string is really exactly and only a number, call both functions and see if they both return true:. The accepted answer for this question has quite a few flaws as highlighted by couple of other users. Try the isNan function :. This function is different from the Number specific Number.

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However, even this one is far from complete. Leading zeros are not handled here, but they do screw the length test. I have tested and Michael's solution is best. Vote for his answer above search this page for "If you really want to make sure that a string" to find it. In essence, his answer is this:. Many of the other solutions fail for these edge cases: ' ', null, "", true, and [].

In theory, you could use them, with proper error handling, for example:. You can use the result of Number when passing an argument to its constructor.

javascript check if string is number

If the argument a string cannot be converted into a number, it returns NaN, so you can determinate if the string provided was a valid number or not. Maybe there are one or two people coming across this question who need a much stricter check than usual like I did. In that case, this might be useful:. This will reject strings like. It's very picky - the string must match the " most minimal perfect form " of the number for this test to pass.

It uses the String and Number constructor to cast the string to a number and back again and thus checks if the JavaScript engine's "perfect minimal form" the one it got converted to with the initial Number constructor matches the original string. Michael suggested something like this although I've stolen "user - John"'s altered version here :.The Number. It returns true if the passed value is an integer, otherwise it return false.

Parameters: This function accepts a single parameter value which specifies the number which the user wants to check for integer.

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Return Value: The number. It will return true if the passed value is of the type Number and an integer, else it returns false.

Passing a number consisting of decimal places as an argument : If a decimal number is passed as argument, the function will return false. Passing a string as an argument : If the argument passed to the Number.

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Is there a command, like IsNumeric or something else, that can identify if a string is a valid number?

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This will return true if input is all numbers. Don't know if it's any better than TryParsebut it will work. It will return true for all Numeric Digits not float and false if input string is any sort of alphanumeric.

Please note : stringTest should not be an empty string as this would pass the test of being numeric. From Benchmarking IsNumeric Options. The TryParse method will try to convert the string to a number integer and if it succeeds it will return true and place the corresponding number in myInt.

If it can't, it returns false. Solutions using the int. Parse someString alternative shown in other responses works, but it is much slower because throwing exceptions is very expensive. Now you do: you should therefore avoid the Parse alternative. If you want to accept decimal numbers, the decimal class also has a. Replace int with decimal in the above discussion, and the same principles apply. You can always use the built in TryParse methods for many datatypes to see if the string in question will pass.

In case you don't want to use int. Parse or double. Parse, you can roll your own with something like this:. I know this is an old thread, but none of the answers really did it for me - either inefficient, or not encapsulated for easy reuse. I also wanted to ensure it returned false if the string was empty or null.

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TryParse returns true in this case an empty string does not cause an error when parsing as a number. So, here's my string extension method:. Or, if you want to test other types of number, you can specify the 'style'. So, to convert a number with an Exponent, you could use:. It is limited by not being able to convert strings that are too big to be contained in a double, but that is a limited requirement and I think if you are working with numbers larger than this, then you'll probably need additional specialised number handling functions anyway.The isNaN function determines whether a value is NaN or not.

Hence, the necessity of an isNaN function. NaN values are generated when arithmetic operations result in undefined or unrepresentable values. Such values do not necessarily represent overflow conditions. A NaN also results from attempted coercion to numeric values of non-numeric values for which no primitive numeric value is available. For example, dividing zero by zero results in a NaN — but dividing other numbers by zero does not. Since the very earliest versions of the isNaN function specification, its behavior for non-numeric arguments has been confusing.

When the argument to the isNaN function is not of type Numberthe value is first coerced to a Number. The resulting value is then tested to determine whether it is NaN.

Thus for non-numbers that when coerced to numeric type result in a valid non-NaN numeric value notably the empty string and boolean primitives, which when coerced give numeric values zero or onethe "false" returned value may be unexpected; the empty string, for example, is surely "not a number.

The function should be interpreted as answering the question, "is this value, when coerced to a numeric value, an IEEE 'Not A Number' value? Even with Number. Alternatively, in the absence of Number. There is a more usage oriented way to think of isNaN : If isNaN x returns falseyou can use x in an arithmetic expression not making the expression return NaN. If it returns truex will make every arithmetic expression return NaN. You can use this, for example, to test whether an argument to a function is arithmetically processable usable "like" a numberor if it's not and you have to provide a default value or something else.

This way you can have a function that makes use of the full versatility JavaScript provides by implicitly converting values depending on context. Get the latest and greatest from MDN delivered straight to your inbox. Sign in to enjoy the benefits of an MDN account.

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The newsletter is offered in English only at the moment. Sign up now. Sign in with Github Sign in with Google. Chrome Full support 1. Edge Full support Firefox Full support 1. IE Full support 3.The Number. It returns true if the passed value is an integer, otherwise it return false. Parameters: This function accepts a single parameter value which specifies the number which the user wants to check for integer.

Return Value: The number. It will return true if the passed value is of the type Number and an integer, else it returns false.

javascript check if string is number

Passing a number consisting of decimal places as an argument : If a decimal number is passed as argument, the function will return false. Passing a string as an argument : If the argument passed to the Number.

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Shubrodeep Banerjee. Check out this Author's contributed articles. Load Comments.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Is there a command, like IsNumeric or something else, that can identify if a string is a valid number? This will return true if input is all numbers. Don't know if it's any better than TryParsebut it will work. It will return true for all Numeric Digits not float and false if input string is any sort of alphanumeric.

Please note : stringTest should not be an empty string as this would pass the test of being numeric. From Benchmarking IsNumeric Options. The TryParse method will try to convert the string to a number integer and if it succeeds it will return true and place the corresponding number in myInt. If it can't, it returns false.

Solutions using the int. Parse someString alternative shown in other responses works, but it is much slower because throwing exceptions is very expensive.

Now you do: you should therefore avoid the Parse alternative. If you want to accept decimal numbers, the decimal class also has a. Replace int with decimal in the above discussion, and the same principles apply.

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You can always use the built in TryParse methods for many datatypes to see if the string in question will pass. In case you don't want to use int. Parse or double. Parse, you can roll your own with something like this:.

javascript check if string is number

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