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I have this javascript function:

  getToken: function () {
        return localStorage.jwtToken;
    },

  this.getToken()!=null //true, 

so basically this function returns "null" instead of null, how can I make the function return the null value?

You probably did:

 localStorage.jwtToken = null;

to set it to null, but as localStorage can only contain string properties, it got stringified to "null". Instead of setting it to null set it to undefined, or just delete the key:

 localStorage.jwtToken = undefined;
 localStorage.removeItem("jwtToken");

JavaScript return Statement, A return statement determines the value the function returns. When control comes across such a statement, it immediately jumps out of the current function and  Function Return. When JavaScript reaches a return statement, the function will stop executing. If the function was invoked from a statement, JavaScript will "return" to execute the code after the invoking statement. Functions often compute a return value.

If instead of "null" you want to return null, return this expression

getToken: function () {
        let token = localStorage.jwtToken;
        return (token === "null") ? null : token;
    }

JavaScript Functions, JavaScript allows functions to return functions, a very powerful technique. return [[expression]]; expression The expression whose value is to be returned. If omitted, undefined is returned instead. Description. When a return statement is used in a function body, the execution of the function is stopped. If specified, a given value is returned to the function caller.

this.getToken()!=null returns true because you are only checking the value.

If you want to check the value and type you need to check with !==.

this.getToken() !== null

Functions :: Eloquent JavaScript, Returning b is returning a function object. In Javascript, functions are just objects, like any other object. If you find that not helpful, just replace the  Calling the function with in a return statement executes the function, and returns whatever value was returned by the function. It is similar to calling var x = b();, but instead of assigning the return value of b() you are returning it from the calling function a().

JavaScript Functions that Return Functions, Returning a value. A function can return a value back into the calling code as the result. The simplest example would be a  JavaScript Return Statement JavaScript provides for passing one value back to the code that called it after everything in the function that needs to run has finished running. JavaScript passes a value from a function back to the code that called it by using the return statement. The value to be returned is specified in the return.

Functions that return a function, A function can optionally accept parameters, and returns one value. Functions in JavaScript are objects, a special kind of objects:  To return a string from a JavaScript function, use the return statement in JavaScript.ExampleYou need to run the following code to learn how to return a string

Functions, This is known as invoking a function. Values can be passed into functions and used within the function. Functions always return a value. In  JavaScript functions have a built-in object called the arguments object. The argument object contains an array of the arguments used when the function was called (invoked). This way you can simply use a function to find (for instance) the highest value in a list of numbers:

Comments
  • Possible duplicate of Storing Objects in HTML5 localStorage
  • How did you set the value? You've confirmed that this.getToken() returns "null"?