null

Null is a type, the only value of which is the value null.

The value null is used when it is necessary to denote the intentional absence of a value of an object (an object with an undefined structure).

A user object is expected, but the structure of this object is currently unclear:

        
          
          let personObj = nullpersonObj = {  name: 'Vasya',  age: 25,}
          let personObj = null

personObj = {
  name: 'Vasya',
  age: 25,
}

        
        
          
            
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null denotes the concepts of "absent" or "value unknown" for an object. It is always explicitly set by the programmer; JavaScript does not automatically establish it.

In JavaScript, null is used only to denote the end of the prototype chain, to show that the next prototype is absent.

There exists a similar primitive value undefined. It denotes that a variable has not yet been assigned a value. They can be easily confused because both denote the absence of a value. The difference is that null denotes an intentional absence of a value of an object (an object without a defined structure), while undefined means that a variable (not an object) has not yet been assigned a value.

For example, JavaScript itself uses undefined to denote uninitialized variables:

        
          
          // A string is expected (not an object)let personNameconsole.log(personName)// undefined// Explicitly stating that the value is absentpersonName = undefined// A user object is expected,// but the structure of this object is currently unclearlet personObj = nullpersonObj = {  name: 'Vasya',  age: 25,  // Job title, string  // Vasya has not yet decided on a profession, so undefined  profession: undefined,}// The function should return an object// If the object cannot be returned, it returns nullfunction returnObject (condition) {  if (condition === true) {    return {      name: 'Vasya',      age: 25,    }  }  // The function could not return an object,  // returning an object with an undefined structure  return null}
          // A string is expected (not an object)
let personName

console.log(personName)
// undefined

// Explicitly stating that the value is absent
personName = undefined

// A user object is expected,
// but the structure of this object is currently unclear
let personObj = null

personObj = {
  name: 'Vasya',
  age: 25,

  // Job title, string
  // Vasya has not yet decided on a profession, so undefined
  profession: undefined,
}

// The function should return an object
// If the object cannot be returned, it returns null
function returnObject (condition) {
  if (condition === true) {
    return {
      name: 'Vasya',
      age: 25,
    }
  }

  // The function could not return an object,
  // returning an object with an undefined structure
  return null
}

        
        
          
            
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          console.log(typeof null)// 'object'
          console.log(typeof null)
// 'object'

        
        
          
            
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          const data = {  users: [] // array of users  success: true // status of the server response}
          const data = {
  users: [] // array of users
  success: true // status of the server response
}

        
        
          
            
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            let data = null  // Some logic  // Waiting for the server response in the form of an object  data = await getUsers()
            let data = null

  // Some logic

  // Waiting for the server response in the form of an object
  data = await getUsers()

        
        
          
            
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