ForEach內功能JavaScript

Question

我無法使用forEach獲得所需的結果。假設下面的代碼產生所期望的結果：

function isEven(array) { 
    var evenNum = []; 
    for (var i = 0; i <= array.length; i++) { 
    if (array[i] % 2 === 0) 
     evenNum.push((array[i])); 

    } 
    return evenNum; 
} 

var output = isEven([1, 4, 5, 6, 10, 13]); 
console.log(output); // --> [4, 6, 10] 

// How do I get the same result with a forEach method? 
// My code reads: 

function isEven(array) { 
    var evenNum = []; 
    array.forEach(function (currentValue) { 
    if (currentValue % 2 === 0) 
     evenNum.push(array[currentValue]); 
    }) 
    return evenNum; 
} 

var output = isEven([1, 4, 5, 6, 10, 13]); 
console.log(output); // --> [10, 10, 10] not desired 

Answer 1

它看起來像您正在索引到陣列中時，你應該直接使用currentValue。

function isEven(array){ 
    var evenNum = []; 
    array.forEach(function(currentValue){ 
     if(currentValue % 2 === 0) 
     evenNum.push(currentValue); 
    }) 
    return evenNum; 
} 

Answer 2

您有evenNum.push(array[currentValue])。它應該是evenNum.push(currentValue)。

function isEven(array) { 
 
    var evenNum = []; 
 
    array.forEach(function (currentValue) { 
 
    if (currentValue % 2 === 0) 
 
     evenNum.push(currentValue); 
 
    }) 
 
    return evenNum; 
 
} 
 

 
var output = isEven([1, 4, 5, 6, 10, 13]); 
 
console.log(output); // --> [10, 10, 10] not desired

Answer 3

var numbers = [1,2,3,4,5,6,7,8,9,10]; 
var even; 

For循環：

even = []; 
for (var i = 0; i < numbers.length; ++i) 
    if (numbers[i] % 2 === 0) 
     even.push(numbers[i]); 
console.log(even); 

及如何使用foreach：

even = []; 
numbers.forEach(n => { 
    if (n % 2 === 0) 
     even.push(n); 
}); 
console.log(even); 

或者更簡潔地說：

even = numbers.filter(n => (n % 2 === 0)); 
console.log(even);