Validate Decimal Numbers in JavaScript - Isnumeric()

Validate decimal numbers in JavaScript - IsNumeric()

@Joel's answer is pretty close, but it will fail in the following cases:

// Whitespace strings:
IsNumeric(' ')    == true;
IsNumeric('\t\t') == true;
IsNumeric('\n\r') == true;

// Number literals:
IsNumeric(-1)  == false;
IsNumeric(0)   == false;
IsNumeric(1.1) == false;
IsNumeric(8e5) == false;

Some time ago I had to implement an IsNumeric function, to find out if a variable contained a numeric value, regardless of its type, it could be a String containing a numeric value (I had to consider also exponential notation, etc.), a Number object, virtually anything could be passed to that function, I couldn't make any type assumptions, taking care of type coercion (eg. +true == 1; but true shouldn't be considered as "numeric").

I think is worth sharing this set of +30 unit tests made to numerous function implementations, and also share the one that passes all my tests:

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

P.S. isNaN & isFinite have a confusing behavior due to forced conversion to number. In ES6, Number.isNaN & Number.isFinite would fix these issues. Keep that in mind when using them.

---

Update :
Here's how jQuery does it now (2.2-stable):

isNumeric: function(obj) {
    var realStringObj = obj && obj.toString();
    return !jQuery.isArray(obj) && (realStringObj - parseFloat(realStringObj) + 1) >= 0;
}

Update :
Angular 4.3:

export function isNumeric(value: any): boolean {
    return !isNaN(value - parseFloat(value));
}

Validate decimal numbers in JavaScript - IsNumeric()

@Joel's answer is pretty close, but it will fail in the following cases:

// Whitespace strings:
IsNumeric(' ')    == true;
IsNumeric('\t\t') == true;
IsNumeric('\n\r') == true;

// Number literals:
IsNumeric(-1)  == false;
IsNumeric(0)   == false;
IsNumeric(1.1) == false;
IsNumeric(8e5) == false;

Some time ago I had to implement an IsNumeric function, to find out if a variable contained a numeric value, regardless of its type, it could be a String containing a numeric value (I had to consider also exponential notation, etc.), a Number object, virtually anything could be passed to that function, I couldn't make any type assumptions, taking care of type coercion (eg. +true == 1; but true shouldn't be considered as "numeric").

I think is worth sharing this set of +30 unit tests made to numerous function implementations, and also share the one that passes all my tests:

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

P.S. isNaN & isFinite have a confusing behavior due to forced conversion to number. In ES6, Number.isNaN & Number.isFinite would fix these issues. Keep that in mind when using them.

---

Update :
Here's how jQuery does it now (2.2-stable):

isNumeric: function(obj) {
    var realStringObj = obj && obj.toString();
    return !jQuery.isArray(obj) && (realStringObj - parseFloat(realStringObj) + 1) >= 0;
}

Update :
Angular 4.3:

export function isNumeric(value: any): boolean {
    return !isNaN(value - parseFloat(value));
}

Check if a number has a decimal place/is a whole number

Using modulus will work:

num % 1 != 0
// 23 % 1 = 0
// 23.5 % 1 = 0.5

---

Note that this is based on the numerical value of the number, regardless of format. It treats numerical strings containing whole numbers with a fixed decimal point the same as integers:

'10.0' % 1; // returns 0
10 % 1; // returns 0
'10.5' % 1; // returns 0.5
10.5 % 1; // returns 0.5

How to properly validate decimal values?

You could test if the string does not start with 2 or more zeroes

^(?!00+\.)[0-9]+\.?[0-9]*$

Regex demo

Note that your pattern ^[0-9]+\.?[0-9]+$ matches at least 2 digits as only the comma is optional.

const rgx = /^(?!00+\.)[0-9]+\.?[0-9]*$/

const cases = ["1234",
  "12.34",
  "0.123",
  "000045",
  "000.45",
  ".45685",
  "5..454",
  "55874.",
  "000000",
  "0.0."
]

cases.forEach(s => console.log(`${s} --> ${rgx.test(s)}`));

Javascript validate number commas and decimal

Try using regex instead

const isNumber = x => !!`${x}`.match(/^\d*(,\d{3})*(\.\d*)?$/)

console.log(isNumber("1,093,222.04")) // true
console.log(isNumber("0.232567")) // true
console.log(isNumber("1267")) // true
console.log(isNumber("1,093,22.04")) // false
console.log(isNumber("1.282,04")) // false
console.log(isNumber("abcd124")) // false

Do note that the function must take in a string, since if you pass in the number itself, the commas , will split the "number" into different parameters

Javascript Check if one decimal number is a multiple of another decimal number

I'm no math wiz so take this with a grain of salt. This appears to be working for me. I tried all the example values in your post and they are all passing as multiples. May or may not work for all values.

const numA = 0.0005;
const numB = 0.0001;

if (Number.isInteger(Math.fround(numA / numB))) {
    console.log('is multiple');
} else {
    console.log('not a multiple');
}

Validate decimal in javascript

Well, this is what I'd do, If I understand correctly.

This addresses a few issues:

• JavaScript doesn't like the numeric value 00.01. Use 0.01 instead
• use parseFloat on your input value. parseInt will round to an integer
• return true if successful (not undefined)

---

function submitform4() {
    var MIN = 0.01;
    var MAX = 100.00;

    var input = document.getElementById('AgeGrade');
    var inputValue = parseFloat(input.value);

    var is_valid = (MIN > inputValue || MAX < inputValue);

    if (is_valid) {
        input.value = inputValue.toFixed(2); // set to 2 decimal places
        return true
    } else {
        alert(inputValue + ' is not between ' + MIN + ' and ' + MAX);
        return false;
    }
}

How to validate if a decimal number is in a sequence 0.001, 0.002, ..., 2.048

Note that doing math with floating point numbers can be inaccurate, so verifying them (which requires an exact value) might not work well.

So, you can multiply your number, so that it's an integer, to avoid precision issues and then you can even use your solution on it.

Here's a purely mathematical solution:

const validate = (toVerify, initial) => {
  const num = toVerify / initial //division is like multiplication with the reciprocal!
  return (num & num - 1) == 0
};

console.log(validate(8, 1)) //true
console.log(validate(0.08, 0.01)) //true
console.log(validate(0.008, 0.001)) //true
console.log(validate(0.016, 0.001)) //true
console.log(validate(0.08, 0.001)) //false

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