将数组转换为逗号分隔的字符串
[英]Convert array to comma separated strings
问题描述
add method of the classList accepts strings only and not an array ( String [, String [, ...]] ) so I wonder if there's an elegant way to convert an array to a list of strings without the obvious looping: 
classList的add方法只接受字符串而不接受数组（ String [, String [, ...]] ）所以我想知道是否有一种优雅的方法可以将数组转换为字符串列表而没有明显的循环：
var breakpoints = {
"extraSmall" : [ "only screen and (max-width: 575px)" ],
"small" : [ "only screen and (min-width: 576px) and (max-width: 767px)" ],
"medium" : [ "only screen and (min-width: 768px) and (max-width: 991px)" ],
"large" : [ "only screen and (min-width: 992px) and (max-width: 1199px)" ],
"extraLarge" : [ "only screen and (min-width: 1200px)" ],
}
Object.keys(breakpoints).map(feature => document.documentElement.classList.add(feature));
Basically, I'm looking to add multiple classes in one call.基本上，我希望在一次调用中添加多个类。
2 个解决方案
解决方案1
2 2019-10-27 08:33:04
Since you don't want to create a new array, don't use .map .由于您不想创建新数组，因此请勿使用.map 。 Rather, you want to perform side-effects, so you should use forEach or a for loop instead:相反，您想要执行副作用，因此您应该使用forEach或for循环：
for (const newClass of Object.keys(breakpoints)) {
document.documentElement.classList.add(newClass)
}
To avoid looping entirely, you could (inelegantly) concatenate with the existing className :为了避免完全循环，您可以（不雅地）与现有的className连接：
document.documentElement.className += ` ${Object.keys(breakpoints).join(' ')}`;
If the <html> tag doesn't already have a class name, the leading space is unnecessary.如果<html>标记还没有 class 名称，则不需要前导空格。 If it's uncertain in advance whether it'll have a class name or not, it'd be easier to use classList.add instead.如果事先不确定它是否具有 class 名称，则改用classList.add会更容易。
解决方案2
1 已采纳 2019-10-27 08:37:48
Since add method accepts multiple classes as parameters you could use spread syntax ... on object keys to pass each element from keys as a class.由于add方法接受多个类作为参数，您可以在 object 键上使用扩展语法...将键中的每个元素作为 class 传递。
var breakpoints = { "extraSmall": [ "only screen and (max-width: 575px)" ], "small": [ "only screen and (min-width: 576px) and (max-width: 767px)" ], "medium": [ "only screen and (min-width: 768px) and (max-width: 991px)" ], "large": [ "only screen and (min-width: 992px) and (max-width: 1199px)" ], "extraLarge": [ "only screen and (min-width: 1200px)" ],} const div = document.querySelector('div'); const classes = Object.keys(breakpoints); div.classList.add(...classes);
<div>Div</div>
For older version of browsers that do not support spread syntax you can use apply method.对于不支持扩展语法的旧版本浏览器，您可以使用apply方法。
var breakpoints = { "extraSmall": [ "only screen and (max-width: 575px)" ], "small": [ "only screen and (min-width: 576px) and (max-width: 767px)" ], "medium": [ "only screen and (min-width: 768px) and (max-width: 991px)" ], "large": [ "only screen and (min-width: 992px) and (max-width: 1199px)" ], "extraLarge": [ "only screen and (min-width: 1200px)" ],} const div = document.querySelector('div'); const classes = Object.keys(breakpoints); div.classList.add.apply(div.classList, classes)
<div>Div</div>
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