javascript 数组中数字的总和 [英] Sum of numbers in an array with javascript

问题描述

我正在尝试获取数组中所有数字的总和.我试图以最简单的方式做到这一点，但总和显示 NAN.为什么会这样?请帮忙

I am trying to get the sum of all the numbers in an array. I am trying to do it in the most simple way but the sum display NAN. why is this so? please help

var numbers = [45, 34, 12, 10, 8, 9];
var i;

for(i=0 ; i<numbers.length; i++){
  var sum = sum + numbers[i];
  //alert(sum);
}
document.getElementById("demo").innerHTML="The sum is" + sum;

<h2>JavaScript</h2>
<p>This example finds the sum of all numbers in an array:</p>
<p id="demo"></p>

推荐答案

您正在为每次循环迭代创建一个新的 sum 变量，并且您也在声明之前使用它，因此 undefined +<some numer> 给你 NaN

You are creating a new sum variable for each loop iteration, also you are using it before it's declared hence undefined + <some numer> giving you NaN

var total = 0;
[45, 34, 12, 10, 8, 9].forEach(num => {total += num});

document.getElementById("demo").innerHTML=`The sum is: ${total}`;

<h2>JavaScript</h2>
<p>This example finds the sum of all numbers in an array:</p>
<p id="demo"></p>

此外，使用 for 循环也不错:

Also, nice hack with for loop:

var total = 0;
var numbers = [45, 34, 12, 10, 8, 9];
for (var i = 0; i < numbers.length; total += numbers[i++]);

console.log('total', total);

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