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Reverse JavaScript Loops

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二05 | 时间 2017 | 作者 红领巾 ] 0人收藏点击收藏

While there's a lot written about javascript loops, reverse JavaScript loops are something that are much less common. It's something that might prove useful though in certain situations. This short article is going to walk you through the process and demonstrate how this can be achieved using on a few lines of JS.

To get started I've added an empty unordered HTML list to the page. This is where the where the content on the array of going to be output as part of the example, just to make it visual on the page:

<ul class="list"></ul>

Next we'll get onto the JavaScript. This is very similar to the standard loop, but with some subtle changes that I'll highlight:

// Create an Array var listArr = [1,2,3,4,5]; for (var i = listArr.length - 1; i >= 0; i--) { $('.list').append('<li>' + listArr[i] + '</li>') }

With this for loop, instead of incrementing the value of i by adding one each time, we're subtracting. So with the length being 5, we first must first subtract 1, before we can increment i by one less each time with i-- with i being greater than or equal to zero. Now I'm sorry if that's a little confusing, I wrote this section a few times, but couldn't think of a better way of explaining what's happening.

If you can explain this better than I have, please leave a comment below and i'll rephrase it.

But to see how it all works together check out the CodePen example below. This probably explains it better than the paragraph above because you can experiment with it and check out for yourself what's going on:

See the Pen Reverse JS Loops by html5andblog ( @html5andblog ) on CodePen .

I hope you've found this article on reverse JavaScript loops useful, and if you ever do use it in a real world scenario we'd love to hear about it. Just leave a comment below.

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