js null undefined 0

console.log('[print null] =>'+null);
console.log('[print undefined] =>'+undefined);
console.log('[print Nan] =>'+undefined);
console.log('[print null==undefined] ==>' + (null == undefined));
console.log('[print null===undefined] ==>' + (null === undefined));
console.log('[print null?true:false] ==>' + (null?true:false));
console.log('[print undefined?true:false] ==>' + (undefined?true:false));
console.log('[print null==0] ==>' + (null==0));
console.log('[print null===0] ==>' + (null===0));
console.log('[print undefined==0] ==>' + (undefined==0));
console.log('[print undefined===0] ==>' + (undefined===0));

index.ios.js:34 [print null] =>null
index.ios.js:35 [print undefined] =>undefined
index.ios.js:36 [print null==undefined] ==>true
index.ios.js:37 [print null===undefined] ==>false
index.ios.js:38 [print null?true:false] ==>false
index.ios.js:39 [print undefined?true:false] ==>false
index.ios.js:40 [print null==0] ==>false
index.ios.js:41 [print null===0] ==>false
index.ios.js:42 [print undefined==0] ==>false
index.ios.js:43 [print undefined===0] ==>false

javascript中的undefined

http://www.cnblogs.com/jamesping/articles/2019602.html