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 。 a
, b
和c
与5
, 10
,和"I am a"
分别让他们不会undefined
。 a
应定义并评估其值为6
testString: 'assert(typeof a === "number" && a === 6, "a
should be defined and evaluated to have the value of 6
");'
- text: 应定义和评估b
的值为15
testString: 'assert(typeof b === "number" && b === 15, "b
should be defined and evaluated to have the value of 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!", "c
should not contain undefined
and should have a value of "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), "Do not change code below the line");'
```