數組迭代：將 forEach 循環重寫為 for 循環

Question

對於一個練習，我必須將此 forEach 循環重寫為一個 for 循環：

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

numbers.forEach(function(number){
  if(number % 3 === 0) {
   console.log(number);
  }
});

我想出了以下內容，但它並沒有真正起作用，因為它給了我未定義：

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

        for(var i = 0; i < numbers.length; i++) {
        if(numbers % 3 === 0) {
        console.log(numbers);
        } 
    };

有人可以向我解釋出了什么問題嗎？

Answer 1

if(numbers[i] % 3 === 0) {
     console.log(numbers[i]);
 } 

Answer 2

您需要第i-th （當前一個）元素numbers ：

 var numbers = [1,2,3,4,5,6,7,8,9,10]; for(var i = 0; i < numbers.length; i++) { if(numbers[i] % 3 === 0) { // ^^^---here console.log(numbers[i]); // ^^^---here } };

Answer 3

您必須使用數字的第 i 個元素。

 var numbers = [1,2,3,4,5,6,7,8,9,10]; for(var i = 0; i < numbers.length; i++) { if(numbers[i] % 3 === 0) { console.log(numbers[i]); } };

Answer 4

 var numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; function fun(number) { if (number % 3 === 0) { console.log(number); } } // Your code with `forEach` numbers.forEach(fun); // Same with for-loop when convert for (var i = 0; i < numbers.length; i++) { fun(numbers[i]); } // you are using `numbers % 3`, numbers is an array and you actually you wanted to use with number (which will be `numbers[i]`