我最近浏览了一些JavaScript代码（由其他人编写），它有类似的内容：
var exports = exports || null;
这是什么意思？这相当于：
var exports = exports ? exports : null;
答案 0 :(得分：0)
除了Or？
之外，JavaScript中的“||”是指什么？
没什么，但它的“或”的定义与其他语言不同。
||运算符计算其左侧操作数，如果该结果是 truthy ，那就是操作的结果;否则，将评估右侧操作数，结果是操作的结果。
因此它不一定会产生布尔值。在您的示例中，exports || null如果它是真实的，则为exports的值，如果不是null则为 <!-- =========================================================== -->
<!-- DataSource -->
<!-- =========================================================== -->
<New id="rfid" class="org.eclipse.jetty.plus.jndi.Resource">
<Arg>jdbc/rfid</Arg>
<Arg>
<New class="org.apache.tomcat.jdbc.pool.DataSource">
<Set name="driverClassName">oracle.jdbc.OracleDriver</Set>
<Set name="url">jdbc:oracle:thin:@integra:1521:integra</Set>
<Set name="username">user</Set>
<Set name="password">password</Set>
<Set name="defaultAutoCommit">false</Set>
<Set name="jmxEnabled">true</Set>
<Set name="testWhileIdle">false</Set>
<Set name="testOnBorrow">true</Set>
<Set name="testOnReturn">false</Set>
<Set name="validationQuery">SELECT 1 FROM dual</Set>
<Set name="validationInterval">30000</Set>
<Set name="minEvictableIdleTimeMillis">30000</Set>
<Set name="timeBetweenEvictionRunsMillis">30000</Set>
<Set name="initialSize">8</Set>
<Set name="minIdle">8</Set>
<Set name="maxIdle">8</Set>
<Set name="maxActive">10</Set>
<Set name="maxWait">30000</Set>
<Set name="removeAbandonedTimeout">120</Set>
<Set name="logAbandoned">true</Set>
<Set name="removeAbandoned">true</Set>
<Set name="jdbcInterceptors">
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReport(threshold=2000);
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReportJmx;
</Set>
</New>
</Arg>
</New>
<New id="myphoto" class="org.eclipse.jetty.plus.jndi.Resource">
<Arg>jdbc/myphoto</Arg>
<Arg>
<New class="org.apache.tomcat.jdbc.pool.DataSource">
<Set name="driverClassName">com.mysql.jdbc.Driver</Set>
<Set name="url">jdbc:mysql://localhost:3306/myphotoipb?zeroDateTimeBehavior=convertToNull&useSSL=false</Set>
<Set name="username">myphoto</Set>
<Set name="password">password</Set>
<Set name="defaultAutoCommit">false</Set>
<Set name="jmxEnabled">true</Set>
<Set name="testWhileIdle">false</Set>
<Set name="testOnBorrow">true</Set>
<Set name="testOnReturn">false</Set>
<Set name="validationQuery">SELECT 1 FROM dual</Set>
<Set name="validationInterval">30000</Set>
<Set name="minEvictableIdleTimeMillis">30000</Set>
<Set name="timeBetweenEvictionRunsMillis">30000</Set>
<Set name="initialSize">2</Set>
<Set name="minIdle">4</Set>
<Set name="maxIdle">8</Set>
<Set name="maxActive">10</Set>
<Set name="maxWait">30000</Set>
<Set name="removeAbandonedTimeout">120</Set>
<Set name="logAbandoned">true</Set>
<Set name="removeAbandoned">true</Set>
<Set name="jdbcInterceptors">
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReport(threshold=2000);
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReportJmx;
</Set>
</New>
</Arg>
</New>
。