Why is my variable undefined JavaScript?
Undefined is also a primitive value in JavaScript. A variable or an object has an undefined value when no value is assigned before using it. So you can say that undefined means lack of value or unknown value. You will get undefined value when you call a non-existent property or method of an object.
Why does JavaScript console say undefined?
It has the side effect of printing to the console. You can observe the same behaviour with many expressions: > var x = 1; undefined; A variable declaration does not produce a value so again undefined is printed to the console.
What does it mean when a variable is undefined?
An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been previously declared by that code. In some programming languages, an implicit declaration is provided the first time such a variable is encountered at compile time.
How do you fix a undefined variable error in JavaScript?
Accessing the variable evaluates to undefined . An efficient approach to solve the troubles of uninitialized variables is whenever possible assign an initial value. The less the variable exists in an uninitialized state, the better.
Why typeof undefined is undefined?
typeof variable === “undefined” in JavaScript. Undefined comes into a picture when any variable is defined already but not has been assigned any value. Undefined is not a keyword. A function can also be undefined when it doesn’t have the value returned.
How do you know if a variable is undefined?
If it is undefined, it will not be equal to a string that contains the characters “undefined”, as the string is not undefined. You can check the type of the variable: if (typeof(something) != “undefined”) …
Is undefined false in JavaScript?
In javascript strict mode, undefined is not false, but javascript try to convert the object or var to a boolean value (this is called in javascript truthy value), that’s the reason you got an undefined as false.
Does undefined return false JavaScript?
The Boolean value of undefined is false. The value of Not only undefined but also null, false, NaN, empty string is also false.
What is the difference between undefined and undefined?
As to what the difference between “undefined” and undefined is: one is a string, the other an object. typeof always returns the type of the variable as a string, because you can redefine undefined to something else so you couldn’t properly compare it anymore, but “undefined” == “undefined” is always true.
What is the difference between undefined and undeclared variables in JavaScript?
Undefined: It occurs when a variable has been declared but has not been assigned with any value. Undeclared: It occurs when we try to access any variable that is not initialized or declared earlier using var or const keyword. …
In what circumstances would a variable have the value undefined?
A variable is said to be ‘undefined’ if it has been declared, but no value has been given to it.
How do you declare an undefined variable in a function?
You can declare a var variable somewhere at the end of the function scope, but still, you can access it before declaration: and you’ll get an undefined. myVariable is accessible and contains undefined even before the declaration line: var myVariable = ‘Initial value’.
Why does the JavaScript Console print undefined when I declare variables?
But none of it explains why the JavaScript console prints undefined when I declare a variable as follows: It prints the result of this expression – which is undefined. And yes, var a is a valid expression on its own. Actually, you should rather be amused by why console prints undefined when you write var a = 3 or something like this.
Why do all the Var and function declaration statements get ignored?
In fact, all the var and function declaration (!) statements seem to be ignored if there’s another statement with some ‘real’ result: >>> var a = 3; undefined >>> var a = 3; a = 4; 4 >>> var a = 3; a = 4; var a = 5; function f () {}; 4 // !!! Now, I suppose the real reason behind is behaviour of eval statement, as described here:
Why does lastbalance = in the inner function set to undefined?
This means that when you do lastBalance = in the inner function, only the third of the variables gets set. No code ever sets the variable in the outside scope. The one in the inner scope is set to undefined every time the function is run. I’m pretty sure you only want the one variable.