javascript - 乘以 JavaScript 变量

Question

当我将一个变量乘以 2 并将该值赋给另一个变量时，为什么会得到 0？基本上，我试图在每次按下按钮时逐渐显示/隐藏 block 。但是，当我执行 count++ * 2 时，它会起作用。

请参阅下面的代码以供引用。

var count = 0,
    num = count * 2;

$('.load').on('click', function() {
   $('.blocks').show();
   $('.blocks').slice(num).hide();
    count++;
});

console.log(num); // num is = to 0

.load {
    display: block;
    margin: 40px 0 0 0;
}

.blocks {
    width: 30px;
    height: 30px;
    background: #000;
    display: inline-block;
    margin: 5px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button class="load">Load this</button>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>
<div class="blocks"></div>

Answer 1

// initial variable initialization
var count = 0,
num = count * 2;

$('.load').on('click', function() {
    $('.blocks').show();
    $('.blocks').slice(num).hide();
    // increment the count value
    count++;
    // re assign a new num value
    num = count * 2;
    console.log(num);
    // num is 0,2,4,6
});

console.log(num); // num is = to 0