forEach trap

Preface: forEach no return value! ! ! Set the return value and no return value.

One, for comparison loop

    var ARR = [ . 1 , 2 , . 3 , . 4 , . 5 ]; 
     
    function Test () { 
        for ( var I = 0 ; I <arr.length; I ++ ) {    
             IF (ARR [I] == . 3 ) {
                 return  ' Found 3, the cycle terminates and ' ; 
            }     
            the console.log (ARR [I]); 
        } 
    } 
    Test ();

Run Results: 1 output. And terminates the cycle. 4, 5 continues to output no later;

 

②、console.log(test());

 

var ARR = [ . 1 , 2 , . 3 , . 4 , . 5 ]; 
 
function Test () { 
    for ( var I = 0 ; I <arr.length; I ++ ) {    
         IF (ARR [I] == . 3 ) {
             return  ' Found 3, the cycle terminates and ' ; 
        }     
        the console.log (ARR [I]); 
    } 
} 
the console.log (Test ());

 

 

Second, in contrast forEach loop

var ARR = [ . 1 , 2 , 3 , . 4 , . 5 ]; 
function test2 () { 
    arr.forEach (function (Item) { 
       IF (Item == 3 ) {
            return  ' found a 3, and this cycle is skipped ' ; 
       } 
       the console.log (Item); 
    });     
} 
test2 ();

The result: the output 1,2,4,5. Did not terminate the loop, but when the item == 3, when, out of this cycle

②、console.log(test2());

 

 ②、console.log(test2());

var ARR = [ . 1 , 2 , 3 , . 4 , . 5 ]; 
function test2 () { 
    arr.forEach (function (Item) { 
       IF (Item == 3 ) {
            return  ' found a 3, and this cycle is skipped ' ; 
       } 
       the console.log (Item); 
    });     
} 
the console.log (test2 ());

The result: the output of 1,2,4,5, undefined. And no output we need, but returned an undefined.

 

 

Third, the solution

 

 Array.some () application

var ARR = [ . 1 , 2 , 3 , . 4 , . 5 ]; 
function Test3 () { 
    arr.some (function (Item) { 
       IF (Item == 3 ) {
            return  ' found 3, and terminates the cycle " ; 
       } 
       the console.log (Item); 
    });     
} 
the console.log (Test3 ());

Run Results: output 1,2, undefined. Termination of the cycle, but no output we need, but returned an undefined.

 

 Array.every () results and some () the same result

Transfer from https://blog.csdn.net/w390058785/article/details/79916266