---
id: 587d824a367417b2b2512c46
title: 了解 JavaScript 断言是如何使用的
challengeType: 2
forumTopicId: 301589
dashedName: learn-how-javascript-assertions-work
---

# --description--

请注意，本项目在 [这个 Repl.it 项目](https://repl.it/github/freeCodeCamp/boilerplate-mochachai) 的基础上进行开发。你也可以从 [GitHub](https://repl.it/github/freeCodeCamp/boilerplate-mochachai) 上克隆。

# --instructions--

使用 assert.isNull() 或 assert.isNotNull() 来让测试通过。

# --hints--

不应有未通过的测试

```js
(getUserInput) =>
  $.get(getUserInput('url') + '/_api/get-tests?type=unit&n=0').then(
    (data) => {
      assert.equal(data.state, 'passed');
    },
    (xhr) => {
      throw new Error(xhr.responseText);
    }
  );
```

请选择正确的断言—isNull 或 isNotNull

```js
(getUserInput) =>
  $.get(getUserInput('url') + '/_api/get-tests?type=unit&n=0').then(
    (data) => {
      assert.equal(data.assertions[0].method, 'isNull', 'Null is null');
    },
    (xhr) => {
      throw new Error(xhr.responseText);
    }
  );
```

You should choose the right assertion - isNull vs. isNotNull.

```js
(getUserInput) =>
  $.get(getUserInput('url') + '/_api/get-tests?type=unit&n=0').then(
    (data) => {
      assert.equal(data.assertions[1].method, 'isNotNull', '1 is not null');
    },
    (xhr) => {
      throw new Error(xhr.responseText);
    }
  );
```

# --solutions--

```js
/**
  Backend challenges don't need solutions, 
  because they would need to be tested against a full working project. 
  Please check our contributing guidelines to learn more.
*/
```