How to "instanceof" a primitive string (string literal) in JavaScript

Question

In JavaScript, I can declare a string in the following ways;

var a = "Hello World";
var b = new String("Hello World");

but a is not an instance of String...

console.log(a instanceof String); //false;
console.log(b instanceof String); //true;

So how do you find the type or "instanceof" a string literal?

Can JavaScript be forced to create a new String() for every string literal?

Solution 1

use typeof "foo" === "string" instead of instanceof.

Solution 2

Use typeof instead and just compare the resulting string. See docs for details.

Solution 3

There is no need to write new String() to create a new string. When we write var x = 'test'; statement, it create the x as a string from a primitive data type. We can't attach the custom properties to this x as we do with object literal. ie. x.custom = 'abc'; x.custom will give undefined value. Thus as per our need we need to create the object. new String() will create an object with typeof() Object and not string. We can add custom properties to this object.

Comments

[jpaugh]

Thanks for the doc link; but instanceof is just as pertinent: "The instanceof operator tests presence of constructor.prototype in object's prototype chain."

[Ninja Coding]

excuse me, could you explain why?

[Artur Udod]

@NinjaCoding basically you can check the link provided at the start of the question stackoverflow.com/questions/203739/…. You'll find a more detailed explanation. But essentially String objects are not primitives, that's the thing. Welcome to js =)

[Hashbrown]

well that's not gonna work if it actually is a String ((function() { return typeof this; }).call('foo'): object), this'll work for both

[user227353]

@NinjaCoding because this answers the first question "So how do you find the type or "instanceof" a string literal?"