javaScript函数-为什么我的默认参数失败？

问题描述：

我的Javascript函数使我的控制台返回我：

My Javascript function leads my console to return me :

TypeError：样式为空

TypeError: style is null

以下是代码段：

let style = {
  one: 1,
  two: 2,
  three: 3
}

function styling(style = style, ...ruleSetStock) {

  return ruleSetStock.map(ruleSet => {
    console.log(ruleSet)
    return style[ruleSet]
  })
}

console.log(styling(null, "one", "two", "three"))

我不明白为什么。在我看来，一切都很棒，

I can't understand why. It seems to me everything is great,

任何提示都会很棒，
谢谢。

Any hint would be great, thanks.

答

默认参数 仅在无值或未定义传递

let defaultStyle = {  one: 1, two: 2, three: 3 }

function styling(style = defaultStyle, ...ruleSetStock) {
  return ruleSetStock.map(ruleSet => {
    return style[ruleSet]
  })
}

console.log(styling(undefined, "one", "two", "three"))

如果我想对所有虚假值（例如false，''，null ）使用默认值怎么办？

What if i want to use default value on all sorts of falsy values such as false, '', null ?

您不能为此使用默认参数，但是可以使用 ||

You can't use default parameter for that but you can use ||

let style1 = {  one: 1, two: 2, three: 3 }

function styling(style, ...ruleSetStock) {
  style = style || style1
  return ruleSetStock.map(ruleSet => {
    return style[ruleSet]
  })
}

console.log(styling(undefined, "one", "two", "three"))
console.log(styling(null, "one", "two", "three"))
console.log(styling('', "one", "two", "three"))
console.log(styling(0, "one", "two", "three"))

javaScript函数-为什么我的默认参数失败？

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