--- id: 56533eb9ac21ba0edf2244aa title: Understanding Uninitialized Variables challengeType: 1 videoUrl: '' localeTitle: 了解未初始化的变量 --- ## Description
声明JavaScript变量时,它们的初始值为undefined 。如果对undefined变量进行数学运算,则结果将为NaN ,表示“非数字” 。如果将字符串与undefined变量连接起来,您将得到一个"undefined"的文字字符串
## Instructions
初始化三个变量abc510 ,和"I am a"分别让他们不会undefined
## Tests
```yml tests: - text: a应定义并评估其值为6 testString: assert(typeof a === 'number' && a === 6); - text: 应定义和评估b的值为15 testString: assert(typeof b === 'number' && b === 15); - text: c不应该包含undefined并且值应为“我是一个字符串!” testString: assert(!/undefined/.test(c) && c === "I am a String!"); - text: 不要更改行下方的代码 testString: assert(/a = a \+ 1;/.test(code) && /b = b \+ 5;/.test(code) && /c = c \+ " String!";/.test(code)); ```
## Challenge Seed
```js // Initialize these three variables var a; var b; var c; // Do not change code below this line a = a + 1; b = b + 5; c = c + " String!"; ```
### After Test
```js console.info('after the test'); ```
## Solution
```js // solution required ```