Does anyone know how can I check whether a variable is a number or a string in JavaScript?
This question is related to
javascript
types
Can you just divide it by 1?
I assume the issue would be a string input like: "123ABG"
var Check = "123ABG"
if(Check == Check / 1)
{
alert("This IS a number \n")
}
else
{
alert("This is NOT a number \n")
}
Just a way I did it recently.
Or just use the invert of isNaN()
:
if(!isNaN(data))
do something with the number
else
it is a string
And yes, using jQuery's $.isNumeric()
is more fun for the buck.
You're looking for isNaN()
:
console.log(!isNaN(123));_x000D_
console.log(!isNaN(-1.23));_x000D_
console.log(!isNaN(5-2));_x000D_
console.log(!isNaN(0));_x000D_
console.log(!isNaN("0"));_x000D_
console.log(!isNaN("2"));_x000D_
console.log(!isNaN("Hello"));_x000D_
console.log(!isNaN("2005/12/12"));
_x000D_
See JavaScript isNaN() Function at MDN.
Since ES2015 the correct way to check if a variable
holds a valid number is Number.isFinite(value)
Examples:
Number.isFinite(Infinity) // false
Number.isFinite(NaN) // false
Number.isFinite(-Infinity) // false
Number.isFinite(0) // true
Number.isFinite(2e64) // true
Number.isFinite('0') // false
Number.isFinite(null) // false
I think converting the var to a string decreases the performance, at least this test performed in the latest browsers shows so.
So if you care about performance, I would, I'd use this:
typeof str === "string" || str instanceof String
for checking if the variable is a string (even if you use var str = new String("foo")
, str instanceof String
would return true).
As for checking if it's a number I would go for the native: isNaN
; function.
uh, how about just:
function IsString(obj) {
return obj !== undefined && obj != null && obj.toLowerCase !== undefined;
}
After further review many months later, this only guarantees obj
is an object that has the method or property name toLowerCase
defined. I am ashamed of my answer. Please see top-voted typeof
one.
Best way to do this:
function isNumber(num) {
return (typeof num == 'string' || typeof num == 'number') && !isNaN(num - 0) && num !== '';
};
This satisfies the following test cases:
assertEquals("ISNUMBER-True: 0", true, isNumber(0));
assertEquals("ISNUMBER-True: 1", true, isNumber(-1));
assertEquals("ISNUMBER-True: 2", true, isNumber(-500));
assertEquals("ISNUMBER-True: 3", true, isNumber(15000));
assertEquals("ISNUMBER-True: 4", true, isNumber(0.35));
assertEquals("ISNUMBER-True: 5", true, isNumber(-10.35));
assertEquals("ISNUMBER-True: 6", true, isNumber(2.534e25));
assertEquals("ISNUMBER-True: 7", true, isNumber('2.534e25'));
assertEquals("ISNUMBER-True: 8", true, isNumber('52334'));
assertEquals("ISNUMBER-True: 9", true, isNumber('-234'));
assertEquals("ISNUMBER-False: 0", false, isNumber(NaN));
assertEquals("ISNUMBER-False: 1", false, isNumber({}));
assertEquals("ISNUMBER-False: 2", false, isNumber([]));
assertEquals("ISNUMBER-False: 3", false, isNumber(''));
assertEquals("ISNUMBER-False: 4", false, isNumber('one'));
assertEquals("ISNUMBER-False: 5", false, isNumber(true));
assertEquals("ISNUMBER-False: 6", false, isNumber(false));
assertEquals("ISNUMBER-False: 7", false, isNumber());
assertEquals("ISNUMBER-False: 8", false, isNumber(undefined));
assertEquals("ISNUMBER-False: 9", false, isNumber(null));
Best way to do that is using isNaN
+ type casting:
Updated all-in method:
function isNumber(n) { return !isNaN(parseFloat(n)) && !isNaN(n - 0) }
The same using regex:
function isNumber(n) { return /^-?[\d.]+(?:e-?\d+)?$/.test(n); }
------------------------
isNumber('123'); // true
isNumber('123abc'); // false
isNumber(5); // true
isNumber('q345'); // false
isNumber(null); // false
isNumber(undefined); // false
isNumber(false); // false
isNumber(' '); // false
The best way I have found is to either check for a method on the string, i.e.:
if (x.substring) {
// do string thing
} else{
// do other thing
}
or if you want to do something with the number check for a number property,
if (x.toFixed) {
// do number thing
} else {
// do other thing
}
This is sort of like "duck typing", it's up to you which way makes the most sense. I don't have enough karma to comment, but typeof fails for boxed strings and numbers, i.e.:
alert(typeof new String('Hello World'));
alert(typeof new Number(5));
will alert "object".
Here's an approach based on the idea of coercing the input to a number or string by adding zero or the null string, and then do a typed equality comparison.
function is_number(x) { return x === x+0; }
function is_string(x) { return x === x+""; }
For some unfathomable reason, x===x+0
seems to perform better than x===+x
.
Are there any cases where this fails?
In the same vein:
function is_boolean(x) { return x === !!x; }
This appears to be mildly faster than either x===true || x===false
or typeof x==="boolean"
(and much faster than x===Boolean(x)
).
Then there's also
function is_regexp(x) { return x === RegExp(x); }
All these depend on the existence of an "identity" operation particular to each type which can be applied to any value and reliably produce a value of the type in question. I cannot think of such an operation for dates.
For NaN, there is
function is_nan(x) { return x !== x;}
This is basically underscore's version, and as it stands is about four times faster than isNaN()
, but the comments in the underscore source mention that "NaN is the only number that does not equal itself" and adds a check for _.isNumber. Why? What other objects would not equal themselves? Also, underscore uses x !== +x
--but what difference could the +
here make?
Then for the paranoid:
function is_undefined(x) { return x===[][0]; }
or this
function is_undefined(x) { return x===void(0); }
jQuery uses this:
function isNumber(obj) {
return !isNaN( parseFloat( obj ) ) && isFinite( obj );
}
Simply use
myVar.constructor == String
or
myVar.constructor == Number
if you want to handle strings defined as objects or literals and saves you don't want to use a helper function.
@BitOfUniverse's answer is good, and I come up with a new way:
function isNum(n) {
return !isNaN(n/0);
}
isNum('') // false
isNum(2) // true
isNum('2k') // false
isNum('2') //true
I know 0
can't be dividend, but here the function works perfectly.
//testing data types accurately in JavaScript (opposed to "typeof")
//from http://bonsaiden.github.com/JavaScript-Garden/
function is(type, obj) {
var clas = Object.prototype.toString.call(obj).slice(8, -1);
return obj !== undefined && obj !== null && clas === type;
}
//basic usage
is('String', 'test'); // true
is('Array', true); // false
Or adapt it to return an unknown type:
function realTypeOf(obj) {
return Object.prototype.toString.call(obj).slice(8, -1);
}
//usage
realTypeOf(999); // 'Number'
May 12, 2012 Update: Full example at Javascript: A Better typeof.
XOR operation can be used to detect number or string. number ^ 0 will always give the number as output and string ^ 0 will give 0 as output.
Example:
1) 2 ^ 0 = 2
2) '2' ^ 0 = 2
3) 'Str' ^ 0 = 0
Errr? Just use regular expressions! :)
function isInteger(val) {
return val.match(/^[0-9]$/)
}
function isFloat(val) {
return val.match(/^[0-9]*/\.[0-9]+$/)
}
What do you thing about this one?
const numberOrString='10'
const isNumber = !isNaN(numberOrString*1)
Created a jsperf on the checking if a variable is a number. Quite interesting! typeof actually has a performance use. Using typeof
for anything other than numbers, generally goes a 1/3rd the speed as a variable.constructor
since the majority of data types in javascript are Objects; numbers are not!
http://jsperf.com/jemiloii-fastest-method-to-check-if-type-is-a-number
typeof variable === 'number'
| fastest | if you want a number, such as 5, and not '5'
typeof parseFloat(variable) === 'number'
| fastest | if you want a number, such as 5, and '5'
isNaN()
is slower, but not that much slower. I had high hopes for parseInt
and parseFloat
, however they were horribly slower.
Very late to the party; however, the following has always worked well for me when I want to check whether some input is either a string or a number in one shot.
return !!Object.prototype.toString.call(input).match(/\[object (String|Number)\]/);
typeof works very well for me in most case. You can try using an if statement
if(typeof x === 'string' || typeof x === 'number') {
console.log("Your statement");
}
where x is any variable name of your choice
For detecting numbers, the following passage from JavaScript: The Good Parts by Douglas Crockford is relevant:
The isFinite function is the best way of determining whether a value can be used as a number because it rejects NaN and Infinity . Unfortunately, isFinite will attempt to convert its operand to a number, so it is not a good test if a value is not actually a number. You may want to define your own isNumber function:
var isNumber = function isNumber(value) { return typeof value === 'number' &&
isFinite(value);
};
You can check the type of variable by using typeof
operator:
typeof variable
The code below returns true for numbers and false for anything else:
!isNaN(+variable);
since a string as '1234' with typeof will show 'string', and the inverse cannot ever happen (typeof 123 will always be number), the best is to use a simple regex /^\-?\d+$/.test(var)
. Or a more advanced to match floats, integers and negative numbers, /^[\-\+]?[\d]+\.?(\d+)?$/
The important side of .test
is that it WON'T throw an exception if the var isn't an string, the value can be anything.
var val, regex = /^[\-\+]?[\d]+\.?(\d+)?$/;
regex.test(val) // false
val = '1234';
regex.test(val) // true
val = '-213';
regex.test(val) // true
val = '-213.2312';
regex.test(val) // true
val = '+213.2312';
regex.test(val) // true
val = 123;
regex.test(val) // true
val = new Number(123);
regex.test(val) // true
val = new String('123');
regex.test(val) // true
val = '1234e';
regex.test(val) // false
val = {};
regex.test(val) // false
val = false;
regex.test(val) // false
regex.test(undefined) // false
regex.test(null) // false
regex.test(window) // false
regex.test(document) // false
If you are looking for the real type, then typeof alone will do.
function IsNumeric(num) {
return ((num >=0 || num < 0)&& (parseInt(num)==num) );
}
This solution resolves many of the issues raised here!
This is by far the most reliable method I have used by far. I did not invent this, and cannot recall where I originally found it. But it works where other techniques fail:
// Begin public utility /getVarType/
// Returns 'Function', 'Object', 'Array',
// 'String', 'Number', 'Boolean', or 'Undefined'
getVarType = function ( data ){
if (undefined === data ){ return 'Undefined'; }
if (data === null ){ return 'Null'; }
return {}.toString.call(data).slice(8, -1);
};
// End public utility /getVarType/
Example of correctness
var str = new String();
console.warn( getVarType(str) ); // Reports "String"
console.warn( typeof str ); // Reports "object"
var num = new Number();
console.warn( getVarType(num) ); // Reports "Number"
console.warn( typeof num ); // Reports "object"
var list = [];
console.warn( getVarType( list ) ); // Reports "Array"
console.warn( typeof list ); // Reports "object"
Try this,
<script>
var regInteger = /^-?\d+$/;
function isInteger( str ) {
return regInteger.test( str );
}
if(isInteger("1a11")) {
console.log( 'Integer' );
} else {
console.log( 'Non Integer' );
}
</script>
Check if the value is a string literal or String object:
function isString(o) {
return typeof o == "string" || (typeof o == "object" && o.constructor === String);
}
Unit test:
function assertTrue(value, message) {
if (!value) {
alert("Assertion error: " + message);
}
}
function assertFalse(value, message)
{
assertTrue(!value, message);
}
assertTrue(isString("string literal"), "number literal");
assertTrue(isString(new String("String object")), "String object");
assertFalse(isString(1), "number literal");
assertFalse(isString(true), "boolean literal");
assertFalse(isString({}), "object");
Checking for a number is similar:
function isNumber(o) {
return typeof o == "number" || (typeof o == "object" && o.constructor === Number);
}
Jsut an FYI, if you're using jQuery you have
$.isNumeric()
to handle this. More details on http://api.jquery.com/jQuery.isNumeric/
the best way i found which also thinks of positive and negative numbers is from : O'Reilly Javascript and DHTML Cookbook :
function isNumber(elem) {
var str = elem.value;
var oneDecimal = false;
var oneChar = 0;
// make sure value hasn't cast to a number data type
str = str.toString( );
for (var i = 0; i < str.length; i++) {
oneChar = str.charAt(i).charCodeAt(0);
// OK for minus sign as first character
if (oneChar = = 45) {
if (i = = 0) {
continue;
} else {
alert("Only the first character may be a minus sign.");
return false;
}
}
// OK for one decimal point
if (oneChar = = 46) {
if (!oneDecimal) {
oneDecimal = true;
continue;
} else {
alert("Only one decimal is allowed in a number.");
return false;
}
}
// characters outside of 0 through 9 not OK
if (oneChar < 48 || oneChar > 57) {
alert("Enter only numbers into the field.");
return false;
}
}
return true;
}
Beware that typeof
NaN
is... 'number'
typeof NaN === 'number'; // true
Simple and thorough:
function isNumber(x) {
return parseFloat(x) == x
};
Test cases:
console.log('***TRUE CASES***');
console.log(isNumber(0));
console.log(isNumber(-1));
console.log(isNumber(-500));
console.log(isNumber(15000));
console.log(isNumber(0.35));
console.log(isNumber(-10.35));
console.log(isNumber(2.534e25));
console.log(isNumber('2.534e25'));
console.log(isNumber('52334'));
console.log(isNumber('-234'));
console.log(isNumber(Infinity));
console.log(isNumber(-Infinity));
console.log(isNumber('Infinity'));
console.log(isNumber('-Infinity'));
console.log('***FALSE CASES***');
console.log(isNumber(NaN));
console.log(isNumber({}));
console.log(isNumber([]));
console.log(isNumber(''));
console.log(isNumber('one'));
console.log(isNumber(true));
console.log(isNumber(false));
console.log(isNumber());
console.log(isNumber(undefined));
console.log(isNumber(null));
console.log(isNumber('-234aa'));
Source: Stackoverflow.com