Here are the quick facts: null is an assigned value. It means nothing. undefined means a variable has been declared but not defined yet.
How to determine if a variable is 'undefined' or 'null'?
JavaScript: Check if Variable is undefined or null
- Introduction. Whether we lose a reference through side-effects, forget to assign a reference variable to an object in memory, or we get an empty response from another resource, database or ...
- Difference Between undefined and null. ...
- Check if Variable is undefined or null. ...
- Using Lodash to Check if Variable is null, undefined or nil. ...
- Conclusion. ...
When is "undefined" equal to "null" in JavaScript?
When you strictly want to check for null in JavaScript, the triple equality operator (===) is the best choice. When you check null === undefined, it returns false – when you strictly check both values, they are not similar. That makes the triple equality operator (===) the recommended operator to check null values in JavaScript.
What is the difference between infinite and undefined?
Some people will say [math]x [/math] is:
- undefined because division by zero is not defined;
- indeterminate because the expression is false;
- infinite because it has to be larger than any finite value;
Can a function return null?
NULL is a valid return value for any function that returns a pointer, regardless of what it points to. /edit just be careful to always check for NULL before dereferencing and to not lose references to dynamically allocated memory.
Is undefined == null?
The undefined value is a primitive value used when a variable has not been assigned a value. The null value is a primitive value that represents the null, empty, or non-existent reference. When you declare a variable through var and do not give it a value, it will have the value undefined.
Is null or undefined better?
null is an assigned value. It means nothing. undefined typically means a variable has been declared but not defined yet. null and undefined are falsy values.
How null == undefined is true?
Summary. undefined is a primitive type of a variable which evaluates falsy, has a typeof() of undefined, and represents a variable that is declared but missing an initial value. null == undefined evaluates as true because they are loosely equal. null === undefined evaluates as false because they are not, in fact, equal ...
Is undefined the same as null math?
undefined has its own data type (undefined), null is only an object. null is treated as 0 in basic arithmetic operations, undefined returns NaN.
Why null is important?
NULL values are used to indicate that you could have a value, but you don't know what that value should be yet. They are placeholders until you finally collect the data needed to fill the table field with a real value. You should never confuse NULL values for zeros or blank strings.
When should I use undefined?
undefined is meant to say that the reference is not existing. A null value has a defined reference to "nothing". If you are calling a non-existing property of an object, then you will get undefined . If I would make that property intentionally empty, then it must be null so you know that it's on purpose.
Why is null == 0 false?
Comparisons convert null to a number, treating it as 0 . That's why (3) null >= 0 is true and (1) null > 0 is false. On the other hand, the equality check == for undefined and null is defined such that, without any conversions, they equal each other and don't equal anything else. That's why (2) null == 0 is false.
Why null === null is true?
2. How to check for null. missingObject === null evaluates to true because missingObject variable contains a null value. If the variable contains a non-null value, like an object, the expression existingObject === null evaluates to false .
Can a number be null?
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.
What is the full meaning of null?
having no valueNull means having no value; in other words null is zero, like if you put so little sugar in your coffee that it's practically null. Null also means invalid, or having no binding force. From the Latin nullus, meaning "not any," poor, powerless null is not actually there at all. Or if it was, it's gone now.
IS null is equal to 0?
The answer to that is rather simple: a NULL means that there is no value, we're looking at a blank/empty cell, and 0 means the value itself is 0.
IS null always defined as 0?
The null pointer constant is always 0. The NULL macro may be defined by the implementation as a naked 0 , or a cast expression like (void *) 0 , or some other zero-valued integer expression (hence the "implementation defined" language in the standard). The null pointer value may be something other than 0.
Is null a good thing?
What is wrong with NULL? The short answer: NULL is a value that is not a value. And that's a problem. It has festered in the most popular languages of all time and is now known by many names: NULL, nil, null, None, Nothing, Nil, nullptr.
Why we should not use null?
The fundamental problem of null is that it is trying to represent the fact that it is not a value while being assigned as a value. This fundamental flaw then snowballs and manifests into problems that we see in everyday production code.
Is it better to use null or empty string?
So, NULL is better. An empty string is useful when the data comes from multiple resources. NULL is used when some fields are optional, and the data is unknown.
Why should nulls be avoided?
They should be avoided to avoid the complexity in select & update queries and also because columns which have constraints like primary or foreign key constraints cannot contain a NULL value.
What is the difference between null and undefined?
There are several differences between null and undefined, which are sometimes understood as the same. Null: It is the intentional absence of the value. It is one of the primitive values of JavaScript. Undefined: It means the value does not exist in the compiler.
What does "undefined" mean in a variable?
Undefined: It means the value does not exist in the compiler. It is the global object. Type: Null: Object. Undefined: undefined. You can see refer to “==” vs “===” article. null == undefined // true null === undefined // false. It means null is equal to undefined but not identical. When we define a variable to undefined then we are trying ...
What does it mean when a variable is null?
It means null is equal to undefined but not identical. When we define a variable to undefined then we are trying to convey that the variable does not exist . When we define a variable to null then we are trying to convey that the variable is empty. Differentiating using isNaN ():
What is the difference between null and undefined in JavaScript?
In JavaScript, null is a primitive value that is used to signify the intentional absence of an object value, whereas undefined is a primitive value that acts as a placeholder for a variable that has not been assigned a value. Null and undefined values are equal when compared using the JavaScript equality operator.
When are null and undefined values equal?
Null and undefined values are equal when compared using the JavaScript equality operator.
Why is it important to understand null and undefined values?
A good understanding of null and undefined values is vital in avoid runtime bugs in your production code. Bugs related to undefined values can be hard to debug and are best avoided. Consider using TypeScript for strongly-typed code that compiles to JavaScript.
How to find the underlying type of a value?
Use the built-in JavaScript function typeof () to find out the underlying type of a value. The function takes a single parameter of the value whose type you want to find.
What does running a similar test on an undefined value give you?
Running a similar test on the undefined value will give you a result of undefined .
Why is null a zero in JavaScript?
As you can see, you can conduct some numeric operations on the null value because it's a number that holds no value. Therefore, it's treated like a zero. Take note that null is not equal to zero in JavaScript, but it is somehow treated like that in this case.
Is JavaScript a type?
JavaScript is a loosely typed language, and because of this, when conducting mathematical operations JavaScript will automatically convert the result to a type it wants. Unfortunately this automatic conversion, which is commonly referred to as type coercion, can bring lots of surprises along with it.
What does "null" and "undefined" mean?
null and undefined are both are used to represent the absence of some value.
What does "undefined" mean in JavaScript?
In JavaScript, undefined means a variable has been declared but has not yet been assigned a value, such as:
What does smart usage off null mean?
Note: the smart usage off null is to be the falsy version of an Object because an Object is always true, and because typeof null return object. That means typeof myVarObject return consistent value for both Object and null type.
What does it mean when a variable is null?
Now you can explicitly assign a variable null. It means that the variable does not have any value. For example - Some people don't have a middle name. So in such a case its better to assign the value null to the middlename variable of a person object.
What does null do?
null use it to empty a value of a variable
What is a non zero value?
A non-zero value is like a holder with roll of toilet tissue and there's tissue still on the tube.
What does it mean when you declare a variable in JavaScript?
When you declare a variable in javascript, it is assigned the value undefined. This means the variable is untouched and can be assigned any value in future. It also implies that you don't know the value that this variable is going to hold at the time of declaration. Now you can explicitly assign a variable null.
What is undefined?
Undefined most typically means a variable has been declared, but not defined. For example:
What are the features of null?
There are two features of null you should understand: 1 null is an empty or non-existent value. 2 null must be assigned.
Is null undefined or undefined?
As you can see so far, null and undefined are different, but share some similarities. Thus, it makes sense that null does not strictly equal undefined. But, and this may surprise you, null loosely equals undefined. In JavaScript, a double equals tests for loose equality and preforms type coercion.
Is null an object?
null and undefined are both primitives. However an error shows that typeof null = object.
