freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/use-conditional-logic-with-if-statements.md

---
id: cf1111c1c12feddfaeb3bdef
title: 用 if 语句来表达条件逻辑
challengeType: 1
videoUrl: 'https://scrimba.com/c/cy87mf3'
forumTopicId: 18348
dashedName: use-conditional-logic-with-if-statements
---

# --description--

`If`语句用于在代码中做条件判断。关键字`if`告诉 JavaScript 在小括号中的条件为真的情况下去执行定义在大括号里面的代码。这种条件被称为`Boolean`条件，因为他们只可能是`true`（真）或`false`（假）。

当条件的计算结果为`true`，程序执行大括号内的语句。当布尔条件的计算结果为`false`，大括号内的代码将不会执行。

**伪代码**

<blockquote>if(<i>条件为真</i>){<br>  <i>语句被执行</i><br>}</blockquote>

**示例**

```js
function test (myCondition) {
  if (myCondition) {
     return "It was true";
  }
  return "It was false";
}
test(true);  // returns "It was true"
test(false); // returns "It was false"
```

当`test`被调用，并且传递进来的参数值为`true`，`if`语句会计算`myCondition`的结果，看它是真还是假。如果条件为`true`，函数会返回`"It was true"`。当`test`被调用，并且传递进来的参数值为`false`，`myCondition`*不* 为`true`，并且不执行大括号后面的语句，函数返回`"It was false"`。

# --instructions--

在函数内部创建一个`if`语句，如果该参数`wasThatTrue`值为`true`，返回`"Yes, that was true"`，否则，并返回`"No, that was false"`。

# --hints--

`trueOrFalse`应该是一个函数。

```js
assert(typeof trueOrFalse === 'function');
```

`trueOrFalse(true)`应该返回一个字符串。

```js
assert(typeof trueOrFalse(true) === 'string');
```

`trueOrFalse(false)`应该返回一个字符串。

```js
assert(typeof trueOrFalse(false) === 'string');
```

`trueOrFalse(true)`应该返回 "Yes, that was true"。

```js
assert(trueOrFalse(true) === 'Yes, that was true');
```

`trueOrFalse(false)`应该返回 "No, that was false"。

```js
assert(trueOrFalse(false) === 'No, that was false');
```

# --seed--

## --seed-contents--

```js
function trueOrFalse(wasThatTrue) {
  // Only change code below this line



  // Only change code above this line

}
```

# --solutions--

```js
function trueOrFalse(wasThatTrue) {
  if (wasThatTrue) {
    return "Yes, that was true";
  }
  return "No, that was false";
}
```