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If I have a declaration as follows:
var j; does j==null until I set it equal to something?
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In JavaScript, function parameters default to undefined . However, it's often useful to set a different default value.
Declaring a JavaScript Variable or: let carName; After the declaration, the variable has no value (technically it is undefined ).
In JavaScript, null is a special value that represents an empty or unknown value. For example, let number = null; The code above suggests that the number variable is empty at the moment and may have a value later.
Basically we can declare variables in three different ways by using var, let and const keyword. Each keyword is used in some specific conditions. var: This keyword is used to declare variable globally. If you used this keyword to declare variable then the variable can accessible globally and changeable also.
No, it has the default value of undefined
But if want to use the !j condition, it will work with both the values (i.e. undefined or null)
Note that (j==null) is true, but (j===null) is false... JavaScript have "falsy" values and sometimes unexpected rules to convert values, plus fancy === operator to compare value and type at the same time.
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