Question

In javascript, using JSDoc, I m querying for an elements on the page:

// @ts-check

/** @type {HTMLInputElement} */
const element = document.getElementById( checkbox );

但我得到警告:

Type HTMLElement | null is not assignable to type HTMLInputElement . Type null is not assignable to type HTMLInputElement .ts(2322)

是否有办法认为这种说法并不无效,正如你在“<条码>上所做的那样?

Answer 1

查阅这些文件后,可在以下网站查阅:。因此,就你而言,正确的法典应当如此:

// @ts-check

const element = /** @type {HTMLInputElement} */ (document.getElementById( checkbox ));

此外,确保在<代码>/** @type{......} */之后,你需要用括号填写你的代码。

Answer 2

这里的最好方式是,你不必总是写出价值的确切类型,更像在多边贸易体系中非致命操作者的方便性:

/**
 * In lieu of writing in TypeScript and having the convenient non-null assertion
 * operator (!), this helper function allows asserting that something is not
 * null or undefined without having to write a JSDoc type cast that has to
 * explicitly know the non-null type (which is error prone).
 *
 * For example, insgtead of having to write this:
 *
 * ```js
 * const value = /** @type {SomeNullableType} */(possiblyNullValue)
 * ```
 *
 * we can write this:
 *
 * ```js
 * const value = NonNull(possiblyNullValue)
 * ```
 *
 * @template {any} T
 * @param {T} item
 */
function NonNull(item) {
    if (item === null || item === undefined) throw  item is null or undefined 
    return item
}

In this example, the type of div will be HTMLDivElement, not HTMLDivElement | null, as desired (plus it will throw if you are actually wrong, which may be even more desirable!):

const div = NonNull(document.querySelector( div ))

• 《联邦法典》中含有且未使用的类型认识的筛选:

友情链接