將數組的某些元素相乘javascript

Question

var valid1=[4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]

function validateCred(array) {
  let doubleArray =0
  for(i=array.length-2; i >= 0; i-=2) {
          doubleArray= array[i]*2
  }
  console.log(doubleArray);      
}

validateCred(valid1)  //prints 8 I want it to print entire loop

我正在嘗試編寫 luhn 算法，這是從后面每第二個數字加倍的第一步，我希望我的結果等於 doubleArray 但是當我嘗試打印它時只打印 8 個

Answer 1

您可以參考下面的代碼來獲得所需的輸出，即從后面開始具有加倍值的數組。

 var valid1=[4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8] function validateCred(array) { let doubleArray = []; for(i=array.length-2; i >= 0; i-=2) { doubleArray.push(array[i] * 2) } return(doubleArray); } console.log(validateCred(valid1))

Answer 2

你只有 8 張照片，因為你有 step i-2 。 另外，請參閱代碼中有關反轉數組的注釋

 const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]; function validateCred(array) { let doubleArray = []; // we should move through all iterations that is why step i-=1 for(let i = array.length-1; i >= 0; i -= 1) { // moving from the end of the array we will get reversed copy if using method push() // that is why changed to unshift() doubleArray.unshift((array.length - 1 - i) % 2 == 0 ? array[i] * 2 : array[i]); // array.length - 1 - i - using because we need to move from right in case length not odd } console.log(doubleArray); } // ES6+ syntax version version function esValidateCred1(array) { const doubleArray = array.reverse().map((i, ind) => ind % 2 === 0 ? i*2 : i).reverse(); console.log(doubleArray);; } validateCred(valid1); esValidateCred1(valid1);

Answer 3

最簡單的方法是對數組使用.map()方法

 var valid1=[4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8] function validateCred(array) { return array.map(item => item*2); } console.log( validateCred(valid1) ) //prints array doubled elements