在arrow函数里面的Typescript，函数参数

Question

在此代码中，我为“bet”添加了一个动作，并将其id作为参数传递给函数。但是当我稍后调用此箭头函数时，this.undoBet的参数等于this.local_bets[this.local_bets.length].bet_id - 循环内传递的最后一个bet_id。

如何使它在每个箭头函数内部this.undoBet保留在该循环中分配给它的bet_id？

for (var k in this.local_bets) {

    var bet = this.local_bets[k];

    if (bet.status == BetStatus.accepted) {

        // Here bet_id is correct for every "bet" variable

        this.addUndo( "undo_bet", () => {

            // When calling this later, bet_id equals to one that belongs to the last bet inside this.local_bets

            this.undoBet( bet.bet_id );
        });

    }

}

Answer 1

一个常见的JavaScript错误。因为for (var k in this.local_bets) {索引在执行连续函数时实际上是 last 。

修复

使用let：

for (let k in this.local_bets) {

    let bet = this.local_bets[k];

更多

此处包含https://basarat.gitbooks.io/typescript/content/docs/let.html

Answer 2

尝试这个（另一个局部变量将在每个新的撤消投注功能中确定范围）：

this.local_bets
    .filter(bet => bet.status == BetStatus.accepted)
    .forEach(bet => this.addUndo("undo_bet", () => this.undoBet(bet.bet_id)));

Answer 3

所有解决方案都不错，但是最好是在不应该更改变量的情况下使用 const 关键字。检查以下代码：

for (const k in this.local_bets) {

const bet = this.local_bets[k];

if (bet.status == BetStatus.accepted) {

    // Here bet_id is correct for every "bet" variable

    this.addUndo( "undo_bet", () => {

        // When calling this later, bet_id equals to one that belongs to the last bet inside this.local_bets

        this.undoBet( bet.bet_id );
    });

}

}