字典——我正在学习 .map .. 但我遇到了这个问题

使用 .map 而不是 for 循环重写下面的示例。

let selectedMonths = [

    { name: 'January', revenue: 10, expenses: 5, quarter: 1 },

    { name: 'February', revenue: 7, expenses: 8, quarter: 1 },

    { name: 'March', revenue: 15, expenses: 3, quarter: 1 }

]

let monthlyProfitLabels = []

for(let i = 0; i < selectedMonths.length; i++){

    let month = selectedMonths[I]

    let label = `${month.name}: ${month.revenue - month.expenses}`

    monthlyProfitLabels.push(label)

}

console.log(monthlyProfitLabels)

他们让我输入的内容 *

let selectedMonths = [

    { name: 'January', revenue: 10, expenses: 5, quarter: 1 },

    { name: 'February', revenue: 7, expenses: 8, quarter: 1 },

    { name: 'March', revenue: 15, expenses: 3, quarter: 1 } 

]

let monthlyProfitLabels = null; // <-- replace null

console.log(monthlyProfitLabels);

到目前为止我输入的内容...

let monthlyProfitLabels = selectedMonths.map(function(month){

  let label = `${month.name}: ${month.revenue - month.expenses}`

    monthlyProfitLabels.push(label) 

})

console.log(monthlyProfitLabels);

它告诉我“无法访问未初始化的变量”..我很困惑......标签之前$和之后都有反引号}，但它们没有显示在这里。