In Typescript, How to check if a string is Numeric
TypescriptTypescript Problem Overview
In Typescript, this shows an error saying isNaN accepts only numeric values
isNaN('9BX46B6A')
and this returns false because parseFloat('9BX46B6A') evaluates to 9
isNaN(parseFloat('9BX46B6A'))
I can still run with the error showing up in Visual Studio, but I would like to do it the right way.
Currently, I have written this modified function -
static isNaNModified = (inputStr: string) => {
var numericRepr = parseFloat(inputStr);
return isNaN(numericRepr) || numericRepr.toString().length != inputStr.length;
}
Typescript Solutions
Solution 1 - Typescript
The way to convert a string to a number is with Number, not parseFloat.
Number('1234') // 1234
Number('9BX9') // NaN
You can also use the unary plus operator if you like shorthand:
+'1234' // 1234
+'9BX9' // NaN
Be careful when checking against NaN (the operator === and !== don't work as expected with NaN). Use:
isNaN(+maybeNumber) // returns true if NaN, otherwise false
Solution 2 - Typescript
Update 2
This method is no longer available in rxjs v6
I'm solved it by using the isNumeric operator from rxjs library (importing rxjs/util/isNumeric
Update
import { isNumeric } from 'rxjs/util/isNumeric';
. . .
var val = "5700";
if (isNumeric(val)){
alert("it is number !");
}
Solution 3 - Typescript
function isNumber(value: string | number): boolean
{
return ((value != null) &&
(value !== '') &&
!isNaN(Number(value.toString())));
}
Solution 4 - Typescript
You can use the Number.isFinite() function:
Number.isFinite(Infinity); // false
Number.isFinite(NaN); // false
Number.isFinite(-Infinity); // false
Number.isFinite('0'); // false
Number.isFinite(null); // false
Number.isFinite(0); // true
Number.isFinite(2e64); // true
Note: there's a significant difference between the global function isFinite() and the latter Number.isFinite(). In the case of the former, string coercion is performed - so isFinite('0') === true whilst Number.isFinite('0') === false.
Also, note that this is not available in IE!
Solution 5 - Typescript
Simple answer: (watch for blank & null)
isNaN(+'111') = false;
isNaN(+'111r') = true;
isNaN(+'r') = true;
isNaN(+'') = false;
isNaN(null) = false;
Solution 6 - Typescript
My simple solution here is:
const isNumeric = (val: string) : boolean => {
return !isNaN(Number(val));
}
// isNumberic("2") => true
// isNumeric("hi") => false;
Solution 7 - Typescript
I would choose an existing and already tested solution. For example this from rxjs in typescript:
function isNumeric(val: any): val is number | string {
// parseFloat NaNs numeric-cast false positives (null|true|false|"")
// ...but misinterprets leading-number strings, particularly hex literals ("0x...")
// subtraction forces infinities to NaN
// adding 1 corrects loss of precision from parseFloat (#15100)
return !isArray(val) && (val - parseFloat(val) + 1) >= 0;
}
Without rxjs isArray() function and with simplefied typings:
function isNumeric(val: any): boolean {
return !(val instanceof Array) && (val - parseFloat(val) + 1) >= 0;
}
You should always test such functions with your use cases. If you have special value types, this function may not be your solution. You can test the function here.
Results are:
enum : CardTypes.Debit : true
decimal : 10 : true
hexaDecimal : 0xf10b : true
binary : 0b110100 : true
octal : 0o410 : true
stringNumber : '10' : true
string : 'Hello' : false
undefined : undefined : false
null : null : false
function : () => {} : false
array : [80, 85, 75] : false
turple : ['Kunal', 2018] : false
object : {} : false
As you can see, you have to be careful, if you use this function with enums.
Solution 8 - Typescript
Considering that your variable could be string or number or any type - for full numbers (non-floats) in Angular/Typescript you can use:
var isFullNumber: boolean =
Number.isInteger(Number(yourVariable)) && yourVariable !== null;
Edited as pointed out by @tarrbal - we CANNOT use just:
Number.isInteger(yourVariable);
To prove check out these 3 tests:
let testVariables = [0, 1, "0", "1", "A", {}, -3, 0.1, NaN, null, undefined];
let isFullNumber: boolean;
let ix: number = 1;
testVariables.forEach(v => {
isFullNumber = Number.isInteger(v); // <---
console.log(ix++, ': ', v, isFullNumber);
})
console.log('--------------');
ix = 1;
testVariables.forEach(v => {
isFullNumber = Number.isInteger(Number(v)); // <---
console.log(ix++, ': ', v, isFullNumber);
})
console.log('--------------');
ix = 1;
testVariables.forEach(v => {
isFullNumber = Number.isInteger(Number(v)) && v !== null; // <---
console.log(ix++, ': ', v, isFullNumber);
})
and these 3 results:
1 : 0 true
2 : 1 true
3 : 0 false <- would expect true
4 : 1 false <- would expect true
5 : A false
6 : {} false
7 : -3 true
8 : 0.1 false
9 : NaN false
10 : null false
11 : undefined false
----------------------------
1 : 0 true
2 : 1 true
3 : 0 true
4 : 1 true
5 : A false
6 : {} false
7 : -3 true
8 : 0.1 false
9 : NaN false
10 : null true <- would expect false
11 : undefined false
----------------------------
1 : 0 true
2 : 1 true
3 : 0 true
4 : 1 true
5 : A false
6 : {} false
7 : -3 true
8 : 0.1 false
9 : NaN false
10 : null false
11 : undefined false
Solution 9 - Typescript
Scrolled through each answer and was surprised that this simple one-liner wasn't presented yet:
const isNumber = (val: string | number) => !!(val || val === 0) && !isNaN(Number(val.toString()));
Solution 10 - Typescript
Most of the time the value that we want to check is string or number, so here is function that i use:
const isNumber = (n: string | number): boolean =>
!isNaN(parseFloat(String(n))) && isFinite(Number(n));
const willBeTrue = [0.1, '1', '-1', 1, -1, 0, -0, '0', "-0", 2e2, 1e23, 1.1, -0.1, '0.1', '2e2', '1e23', '-0.1', ' 898', '080']
const willBeFalse = ['9BX46B6A', "+''", '', '-0,1', [], '123a', 'a', 'NaN', 1e10000, undefined, null, NaN, Infinity, () => {}]
Solution 11 - Typescript
My solution:
function isNumeric(val: unknown): val is string | number {
return (
!isNaN(Number(Number.parseFloat(String(val)))) &&
isFinite(Number(val))
);
}
// true
isNumeric("-10");
isNumeric("0");
isNumeric("0xff");
isNumeric("0xFF");
isNumeric("8e5");
isNumeric("3.1415");
isNumeric("+10");
isNumeric("144");
isNumeric("5");
// false
isNumeric("-0x42");
isNumeric("7.2acdgs");
isNumeric("");
isNumeric({});
isNumeric(NaN);
isNumeric(null);
isNumeric(true);
isNumeric(Infinity);
isNumeric(undefined);
isNumeric([]);
isNumeric("some string");
Solution 12 - Typescript
const isNumeric = (value: string): boolean =>
!new RegExp(/[^\d]/g).test(value.trim());
If you want to allow decimal point
const isNumeric = (value: string): boolean =>
!new RegExp(/[^\d.]/g).test(value.trim());
Solution 13 - Typescript
if var sum=0; var x;
then, what about this? sum+=(x|0);
Solution 14 - Typescript
Whether a string can be parsed as a number is a runtime concern. Typescript does not support this use case as it is focused on compile time (not runtime) safety.