indicator.indicator_threshold![index] = threshold;也报错Element implicitly has an 'any' type because expression of type 'number' can't be used to index type 'number | (number | null)[]'.

这个报错是因为 TypeScript 不确定 `indicator_threshold` 属性的类型。可以在定义 `indicator_threshold` 属性时加上类型，例如：

interface Indicator {
  indicator_threshold: (number | null)[];
}

let indicator: Indicator = { indicator_threshold: [] };

const index = 0;
const threshold = 10;

indicator.indicator_threshold[index] = threshold;

这样 TypeScript 就能够正确推断 `indicator_threshold` 属性的类型，并且就不会报错了。