freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/understanding-uninitialized-variables.chinese.md

id, title, challengeType, videoUrl, localeTitle

id	title	challengeType	videoUrl	localeTitle
56533eb9ac21ba0edf2244aa	Understanding Uninitialized Variables	1		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a ， b和c与5 ， 10 ，和"I am a"分别让他们不会undefined 。

Tests

tests:
  - text: <code>a</code>应定义并评估其值为<code>6</code>
    testString: 'assert(typeof a === "number" && a === 6, "<code>a</code> should be defined and evaluated to have the value of <code>6</code>");'
  - text: 应定义和评估<code>b</code>的值为<code>15</code>
    testString: 'assert(typeof b === "number" && b === 15, "<code>b</code> should be defined and evaluated to have the value of <code>15</code>");'
  - text: <code>c</code>不应该包含<code>undefined</code>并且值应为“我是一个字符串！”
    testString: 'assert(!/undefined/.test(c) && c === "I am a String!", "<code>c</code> should not contain <code>undefined</code> 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");'

Challenge Seed

// 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

console.info('after the test');

Solution

// solution required