Question

//No issues in below:
let a = [1, 2, 3, 4, 5];

for (let i of a) {
    document.write('<br />' + i); //1 2 3 4 5
}
// +++++++++++++++++++++++++++++++++++++++++++++++++++++++++

//No issues in below either
function add(...numbers: number[]): number {
    let temp: number = 0;
    for (var i: number = 0; i < numbers.length; i++) {
        temp += numbers[i];
    }
    return temp;
}

let result: number = add(1,5,8); 
document.body.innerHTML = `Result = ${result}`; //Result = 14
// +++++++++++++++++++++++++++++++++++++++++++++++++

// Hmm! Undefined
function add(...numbers: number[]): number {
    let temp: number = 0;
    for (let i of numbers) {
        temp += numbers[i];
    }
    return temp;
}

let result: number = add(1,5,8); 
document.body.innerHTML = `Result = ${result}`; // Result = NaN

我正在尝试使用＃34;＆＃34; forScript中的for循环。但是，没有像我预期的那样工作。例如，在最后一次尝试中我得到了＆＃34; NaN＆＃34;当我被期望获得14时的价值。我做错了什么？

Answer 1

for (... of ...)语法产生数组的实际元素，而不是索引。因此，正确的JavaScript语法就是：

function add(...numbers) {
    let sum = 0;
    for (let i of numbers) {
        sum += i;
    }
    return sum;
}

（添加类型注释以获取TypeScript。）

当然，由于numbers是一个数组，因此ES6也允许你用单行代码执行此操作：

add = (...numbers) => numbers.reduce((x, y) => x + y, 0)

我如何在TypeScript中使用for循环？

1 个答案: