freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-algorithm-scripting/truncate-a-string.md

---
id: ac6993d51946422351508a41
title: 截断字符串
challengeType: 5
forumTopicId: 16089
dashedName: truncate-a-string
---

# --description--

如果传入的字符串（第一个参数）的长度大于传入的值（第二个参数），请在这个位置截断它， 并在后面加上 `...`，然后返回结果。

# --hints--

`truncateString("A-tisket a-tasket A green and yellow basket", 8)` 应返回 `A-tisket...`。

```js
assert(
  truncateString('A-tisket a-tasket A green and yellow basket', 8) ===
    'A-tisket...'
);
```

`truncateString("Peter Piper picked a peck of pickled peppers", 11)` 应返回 `Peter Piper...`。

```js
assert(
  truncateString('Peter Piper picked a peck of pickled peppers', 11) ===
    'Peter Piper...'
);
```

`truncateString("A-tisket a-tasket A green and yellow basket", "A-tisket a-tasket A green and yellow basket".length)` 应返回 `A-tisket a-tasket A green and yellow basket`。

```js
assert(
  truncateString(
    'A-tisket a-tasket A green and yellow basket',
    'A-tisket a-tasket A green and yellow basket'.length
  ) === 'A-tisket a-tasket A green and yellow basket'
);
```

`truncateString("A-tisket a-tasket A green and yellow basket", "A-tisket a-tasket A green and yellow basket".length + 2)` 应返回 `A-tisket a-tasket A green and yellow basket`。

```js
assert(
  truncateString(
    'A-tisket a-tasket A green and yellow basket',
    'A-tisket a-tasket A green and yellow basket'.length + 2
  ) === 'A-tisket a-tasket A green and yellow basket'
);
```

`truncateString("A-", 1)` 应返回字符串 `A...`。

```js
assert(truncateString('A-', 1) === 'A...');
```

`truncateString("Absolutely Longer", 2)` 应返回 `Ab...`。

```js
assert(truncateString('Absolutely Longer', 2) === 'Ab...');
```

# --seed--

## --seed-contents--

```js
function truncateString(str, num) {
  return str;
}

truncateString("A-tisket a-tasket A green and yellow basket", 8);
```

# --solutions--

```js
function truncateString(str, num) {
  if (num >= str.length) {
    return str;
  }

  return str.slice(0, num) + '...';
}

truncateString("A-tisket a-tasket A green and yellow basket", 8);
```