What is typeof undefined in JavaScript?
A variable that has not been assigned a value is of type undefined . A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned .
Is undefined equal to null JavaScript?
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. This means we compare two values after converting them to a common type.
Why null == undefined is true in JavaScript?
null and undefined both return false . That’s why your code is actually checking if false is equal to false . However their types are not equal. Because of that, the next statement will return false, as the === comparison operator checks both the types and their value.
Is it better to return null or undefined?
More generally any function returning an object should return null when the intended object does not exist. Because it could exist given another input/state/context. undefined implicitly represents the absence of meaning of that value in your application’s context.
Is it better to use null or undefined JavaScript?
Only use null if you explicitly want to denote the value of a variable as having “no value”. As @com2gz states: null is used to define something programmatically empty. undefined is meant to say that the reference is not existing. A null value has a defined reference to “nothing”.
How do I check if a Typecript is undefined?
You can check if it’s is undefined first. In typescript (null == undefined) is true. This is only half correct: 1) null and undefined DO have types in TypeScript.
Is typeof undefined?
Here the assigned variables don’t have any value but the variable exists. Here the type of variable is undefined. If you assigned a value(var geeks === undefined ) it will show, if not it will also show undefined but in different meaning. Here the undefined is the typeof undefined.
Is null better than undefined?
null is a special value meaning “no value”. null is a special object because typeof null returns ‘object’. On the other hand, undefined means that the variable has not been declared, or has not been given a value.
Is it OK to return null in JavaScript?
More generally any function returning an object should return null when the intended object does not exist. Because it could exist given another input/state/context. null represents the absence of value for a given input/state/context.