javaScript函数-为什么我的默认参数失败? [英] javaScript function - why my default argument fails?
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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.
推荐答案
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"))
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