How can I detect if a variable is a string?
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1You might want to use underscore.js, it has methods for this built in documentcloud.github.com/underscore/#isString - in case of isString it uses the method mentioned by user113716Martin Wawrusch– Martin Wawrusch2012-03-09 15:08:44 +00:00Commented Mar 9, 2012 at 15:08
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2possible duplicate of Check if a variable is a stringPhilipp Kyeck– Philipp Kyeck2014-02-23 22:06:46 +00:00Commented Feb 23, 2014 at 22:06
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possible duplicate of Check whether variable is number or string in javascriptJonathan Hall– Jonathan Hall2015-08-21 20:12:54 +00:00Commented Aug 21, 2015 at 20:12
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9 Answers
This is the way specified in the ECMAScript spec to determine the internal [[Class]] property.
if( Object.prototype.toString.call(myvar) == '[object String]' ) {
// a string
}
From 8.6.2 Object Internal Properties and Methods:
The value of the [[Class]] internal property is defined by this specification for every kind of built-in object. The value of the [[Class]] internal property of a host object may be any String value except one of "Arguments", "Array", "Boolean", "Date", "Error", "Function", "JSON", "Math", "Number", "Object", "RegExp", and "String". The value of a [[Class]] internal property is used internally to distinguish different kinds of objects. Note that this specification does not provide any means for a program to access that value except through Object.prototype.toString (see 15.2.4.2).
For an example of how this is useful, consider this example:
var str = new String('some string');
alert( typeof str ); // "object"
alert( Object.prototype.toString.call(str) ); // "[object String]"
If you use typeof, you get "object".
But if you use the method above, you get the correct result "[object String]".
1 Comment
jackwanders
not sure why this is the accepted answer. objects are not strings.
new String() results in an object containing a series of indexed properties, each with a value corresponding to the character at that position. Yes, it will get coerced into a string via Object's toString method, but the fact remains that new String('some string') is not a string, in and of itself. typeof someString === "string" is the correct way to determine if a variable is a string. Whether a variable can be turned into a string is moot; every object that can trace its prototype chain to Object has toStringYou can use typeof to do it, but for a lot of things this is bad design.
if (typeof myVar == "string") {
alert("I'm a string!");
}
1 Comment
Daniel DiPaolo
Depends on what you're trying to do. Typically you should know what type you're receiving or it shouldn't matter (ie, you'll do the same thing to it regardless of the type).
Use typeof.
if (typeof foo == 'string')
1 Comment
crdx
Probably clearer not to use keywords as variables in examples.
I don't think we need to treat new String('some string') as a string, because if we try:
new String('abc')==='abc'
It will return false!
But if we try:
String('abc')==='abc'
It will return true.
Comments
var str = new String("some string");
if(str.constructor.name === "String")
{
alert("I'm a string!");
}
or simply:
if(str.constructor === String)
{
alert("I'm a string!");
}
Comments
typeof('yourstring');// returns string
Comments
Use alert(typeof "hello");
alert(typeof 123);
Ref.: here.
Comments
('str'.constructor === String) && alert('its a string!');
Comments
2 Comments
Lijesh Shakya
I got an Reference Error
_ is not defined. Could you specify whether it requires package / specific jQuery version?
Diego Cotini
I mentioned that "Using underscore". Underscore is a JS Library: underscorejs.org/#notes
