JS Null empty judgment

 

JS determine whether the object is empty 

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How to determine whether a JS array is empty if it contains a value? The following methods can not determine whether the object is 0, null, undefined

 1 .js determine whether the array is empty? 

ARR the let = [];
 IF (arr.length == 0 ) { 
   the console.log ( "empty array" ) 
} the else { 
   the console.log ( "array is not empty" ) 
}

 2 . determines whether the array contains a JS value? 
Method a: arr.indexOf () 
IF (! Arr.indexOf (2) = -1 ) { 
   the console.log ( "array containing 2" ) 
} the else { 
   the console.log ( "array excluding 2" ) 
} 

Method two: for determining if binding loop 
for (the let I = 0; I <arr.length; I ++ ) {
   IF (ARR [I] === 2 ) { 
      the console.log ( "array containing 2 ' ) 
　　} 
} 

Method three: arr.find (the callback)    
arr.find (value => {
    IF (value === 2 ) { 
      the console.log ( "array containing 2 ' ) 
　　} 
}) 

method IV: arr.includes () returns true array contains a certain value, no returns false. ES7 new methods. 

ARR the let = [1,2,3,4 ];
 IF (arr.includes (2 )) { 
  the console.log ( "array with a 2" ); 
} the else { 
  the console.log ( "no array 2" ); 
}