javascript - 当我使用 let 声明时，初始化区域中语句的语义

Question

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Answer 1

使用 let 时，i 被声明一次，并在每个循环中获得一个新的绑定(bind)。并且其范围仅在 block 语句内部可见。

从这里Variables and scoping in ECMAScript 6 :

let in loop heads

In loops, you get a fresh binding for each iteration if you let-declare a variable. The loops that allow you to do so are: for, for-in and for-of.

for (let i = 0; i < 3; i++) {
    let x = 1;
    setTimeout(() => console.log(i), 1000);
}

另一个带有赋值的示例，用于重新绑定(bind)。

for (let x = { v: 0 }; x.v < 2; x.v += 1) {
    setTimeout(() => console.log(x), 100); // same values
}

for (let x = { v: 0 }; x.v < 2; x = { v: x.v + 1}) {
    setTimeout(() => console.log(x), 100); // different values
}

.as-console-wrapper { max-height: 100% !important; top: 0; }