为什么它输出未定义?

Question

这是我的代码：

var arr = [];
class Art {
constructor() {
this.values = Array();
}
add(date, amount, currency, product) {
this.values.push([date, amount, currency, product].toString());
}
list() {
return this.values;
}
clear(date) {
for (let i = this.values.length - 1; i >= 0; --i) {
if (this.values[i][0] == date) {
this.values.splice(i, 1);
}
}
}
total() {
return this.values[this.amount + this.currency];
}
}
const art = new Art();
art.add('2017-04-25', 2, 'USD', 'Jogurt');
art.add('2017-04-25', 3, 'USD', 'French fries');
art.add('2017-04-27', 4.75, 'USD', 'Beer');
art.clear('2017-04-27');
console.log(art.list());
console.log(art.total());

total((; 应该返回我添加到 art.add 的金额和货币。但它输出未定义。我已经尽力而为。但是所有时候我都有未定义或 NaN。你能帮帮我吗？

Answer 1

您需要将值存储在数组中，而不是数据数组的字符串表示形式中。

要保留金额，您可以在插入新数据集时添加金额，或者在拼接项目时删除值。

this.totals实现为一个对象，货币作为键，值作为金额。

class Art {
constructor() {
this.values = Array();
this.totals = Object.create(null);
}
add(date, amount, currency, product) {
this.totals[currency] = this.totals[currency] || 0;
this.totals[currency] += amount;
this.values.push([date, amount, currency, product]); //.toString());
}
list() {
return this.values;
}
clear(date) {
var amount, currency;
for (let i = this.values.length - 1; i >= 0; --i) {
if (this.values[i][0] == date) {
[, amount, currency] = this.values.splice(i, 1)[0]
this.totals[currency] -= amount;
}
}
}
total() {
return this.totals;
}
}
const art = new Art();
art.add('2017-04-25', 2, 'USD', 'Jogurt');
art.add('2017-04-25', 3, 'USD', 'French fries');
art.add('2017-04-27', 4.75, 'USD', 'Beer');
art.clear('2017-04-27');
console.log(art.list());
console.log(art.total());