計算空屬性值-有解無憂

我在下面有一個簡單的 for 回圈，我將在其中檢查具有空值的特定屬性。我想計算空值的總數并將它們存盤在一個變數中，該變數應該是 7。我一直將空值轉換為 0 或未定義。

const test = [
    {
        'theKey': null,
        'theName': 'bill'
    },
    {
        'theKey': null,
        'theName': 'jon'
    },
    {
        'theKey': null,
        'theName': 'theo'
    },
    {
        'theKey': null,
        'theName': 'rich'
    },
    {
        'theKey': null,
        'theName': 'rigo'
    },
    {
        'theKey': null,
        'theName': 'cleo'
    },
    {
        'theKey': null,
        'theName': 'jill'
    },
]

for (var i = 0; i < test.length; i  ) {
    const theValues = test[i]['theKey']
    console.log(theValues)
}

我試過了...

console.log(theValues.length)

和

for (var i = 0; i < test.length; i  ) {
    const theValues = test[i]['theKey']
    const theSum = _.sum(theValues)
    // console.log(theValues)

    console.log(theSum)
}

uj5u.com熱心網友回復：

使用for-loop：

const test = [ { 'theKey': null, 'theName': 'bill' }, { 'theKey': null, 'theName': 'jon' }, { 'theKey': null, 'theName': 'theo' }, { 'theKey': null, 'theName': 'rich' }, { 'theKey': null, 'theName': 'rigo' }, { 'theKey': null, 'theName': 'cleo' }, { 'theKey': null, 'theName': 'jill' } ];

let count = 0;
for (var i = 0; i < test.length; i  ) {
  if (test[i]['theKey'] === null) {
    count  ; 
  }
}

console.log(count);

使用Array#reduce：

const test = [ { 'theKey': null, 'theName': 'bill' }, { 'theKey': null, 'theName': 'jon' }, { 'theKey': null, 'theName': 'theo' }, { 'theKey': null, 'theName': 'rich' }, { 'theKey': null, 'theName': 'rigo' }, { 'theKey': null, 'theName': 'cleo' }, { 'theKey': null, 'theName': 'jill' } ];

const count = test.reduce((total, { theKey }) => 
  theKey === null ? total   1 : total
, 0);

console.log(count);

uj5u.com熱心網友回復：

theValues不是陣列，它沒有長度。它也是for回圈本地的，所以你不能在回圈之后訪問它。

不需要陣列，只需增加一個計數器變數。

let nullCount = 0;
for (let i = 0; i < test.length; i  ) {
    if (test[i].theKey === null) {
        nullCount  ;
    }
}
console.log(nullCount);

uj5u.com熱心網友回復：

const test = [
    {
        'theKey': null,
        'theName': 'bill'
    },
    {
        'theKey': null,
        'theName': 'jon'
    },
    {
        'theKey': null,
        'theName': 'theo'
    },
    {
        'theKey': null,
        'theName': 'rich'
    },
    {
        'theKey': null,
        'theName': 'rigo'
    },
    {
        'theKey': null,
        'theName': 'cleo'
    },
    {
        'theKey': null,
        'theName': 'jill'
    },
];

let count = 0;
for (var i = 0; i < test.length; i  ) {
    if(test[i]['theKey'] == null){
    count  ;
    }
}
    console.log(count);

轉載請註明出處，本文鏈接：https://www.uj5u.com/qukuanlian/359062.html

標籤：javascript 节点.js

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