When I execute below code , it prints "undefined" two times. I was expecting that it would raise error since variable is not defined and also there is use strict' statement in the top.
'use strict';
var a;
console.log(typeof a);
console.log(typeof b);
Can anyone explain why it is not raising an error ?
In fact in JavaScript undefined means that the variable isn't yet defined, so basically :
typeof a returns undefined because the variable a was only declared but not initialized yet (there's no value assigned to it).
And typeof b returns undefined because the variable b is not yet declared, so isn't defined.
And if there's no value assigned to a variable, it gets the type undefined because as type can't be determined.
So if you check the MDN typeof specification you will see that :
The
typeofoperator returns a string indicating the type of the unevaluated operand, and if you see types table you can see thatundefinedis a primitive type and one of the possible return values oftypeof.
Examples:
And you can see in the Examples section, the undefined return:
// Undefined
typeof undefined === 'undefined';
typeof declaredButUndefinedVariable === 'undefined';
typeof undeclaredVariable === 'undefined';
Note:
And as stated in comments this is only related to JavaScript syntax and doesn't have anything to do with nodejs.
You don't use a function from "a", nor do you use any functions wich excepts a parameter, wich isn't undefined. Typeof only checks for the memory location of the variable.
undefined is a primitive data type,
and that's one of the possible options the typeof operator can return,
the other options it can return are:
boolean numberstringfunctionobjectsymbol
undefinedmeans that the variable isn't yet defined, that's the normal behavior.node.js.. Will behave exactly same in the browser!