Question

我已经阅读了其他有关for-of循环的问题，并想出了这段代码来计算数组中所有元素的平均值和总和，似乎有些不正确，将不胜感激。：

var i;
elmt=[]
elmt[0] = 0;
elmt[1] = 1;
elmt[2] = 2;
elmt[3] = 3;
elmt[4] = 4;
elmt[5] = 7;
elmt[6] = 8;
elmt[7] = 9;
elmt[8] = 10;
elmt[9] = 11;

var sum = 0;
for (let sum of elmt) {
    sum += parseInt( elmt[i], 10 ); 
}
var avg = sum/elmt.length;

document.write( "The sum of all the elements is: " + sum + " The average is: " + avg );

<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Loops</h2>

<p id="demo"></p>

</body>
</html>

如果您知道其他使用“ for-of”循环执行相同操作的简便方法，请随时分享。

Answer 1

您正在使用两种循环。您可以选择普通的for循环，也可以选择for...of循环：

// For loop
for (i = 0; i < elms.length; i++) { 
  sum += elmt[i];
}

// For...of loop
for (let e of elmt) { 
  sum += e;
}

但是，a cleaner way是通过使用reduce：

var sum = elms.reduce((a, c) => a + c, 0);
var avg = sum / elms.length;

Answer 2

尝试以下

var elmt = [0,1,2,3,4,7,8,9,10,11];

//Using reduce()

function totalReduce(arr) {
  if(!Array.isArray(arr)) return;
  return arr.reduce((a, v)=>a + v);
}

//Using for loop

function totalForLoop(arr) {
  if(!Array.isArray(arr)) return;
  let totalNumber = 0;
  for (let i=0,l=arr.length; i<l; i++) {
     totalNumber+=arr[i];
  }
  return totalNumber;
}
// Using while loop

function totalWhile(arr) {
  if(!Array.isArray(arr)) return;
  let totalNumber = 0, i=-1;
  while (++i < arr.length) {
     totalNumber+=arr[i];
  }
  return totalNumber;
}
// Using array forEach

function totalForEach(arr) {
  if(!Array.isArray(arr)) return;
  let sum=0;
  arr.forEach(each => {
    sum+=each;
  });
  return sum;
};


var sum = totalReduce(elmt);

console.log( "Sum Using reduce: " + sum + " Average: " + sum/elmt.length );

sum = totalForLoop(elmt);
console.log( "Sum Using totalForLoop: " + sum + " Average: " + sum/elmt.length );

sum = totalWhile(elmt);
console.log( "Sum Using totalWhile: " + sum + " Average: " + sum/elmt.length );

sum = totalForEach(elmt);
console.log( "Sum Using totalForEach: " + sum + " Average: " + sum/elmt.length );

reduce（）方法在数组的每个成员上执行（提供的）reduce函数，从而产生单个输出值。

Answer 3

      _handleAppStateChange = (nextAppState) => {
if (this.state.appState.match(/inactive|background/) && nextAppState === 'active') {
  console.log('App has come to the foreground!')
  this.setState({appState: AppState.currentState});
} 
else if (this.state.appState.match(/active|background/) && nextAppState === 'inactive') {
  console.log('App has gone to background!')
   this.setState({appState: AppState.currentState});
}

假设所有元素都是数字，否则您需要进行类型检查以忽略NaN条目。

使用for-of循环的数组中所有元素的总和/平均值

3 个答案: