{"action":"opened","issue":{"url":"https://api.github.com/repos/cobus07/front-end-knowledge-list/issues/1","repository_url":"https://api.github.com/repos/cobus07/front-end-knowledge-list","labels_url":"https://api.github.com/repos/cobus07/front-end-knowledge-list/issues/1/labels{/name}","comments_url":"https://api.github.com/repos/cobus07/front-end-knowledge-list/issues/1/comments","events_url":"https://api.github.com/repos/cobus07/front-end-knowledge-list/issues/1/events","html_url":"https://github.com/cobus07/front-end-knowledge-list/issues/1","id":171094631,"number":1,"title":"null与undefined","user":{"login":"cobus07","id":13163289,"avatar_url":"https://avatars.githubusercontent.com/u/13163289?v=3","gravatar_id":"","url":"https://api.github.com/users/cobus07","html_url":"https://github.com/cobus07","followers_url":"https://api.github.com/users/cobus07/followers","following_url":"https://api.github.com/users/cobus07/following{/other_user}","gists_url":"https://api.github.com/users/cobus07/gists{/gist_id}","starred_url":"https://api.github.com/users/cobus07/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/cobus07/subscriptions","organizations_url":"https://api.github.com/users/cobus07/orgs","repos_url":"https://api.github.com/users/cobus07/repos","events_url":"https://api.github.com/users/cobus07/events{/privacy}","received_events_url":"https://api.github.com/users/cobus07/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2016-08-15T01:45:41Z","updated_at":"2016-08-15T01:45:41Z","closed_at":null,"body":"null表示\"没有对象\"，即该处不应该有值。\r\n（1） 作为函数的参数，表示该函数的参数不是对象。\r\n（2） 作为对象原型链的终点。\r\n\r\n`Object.getPrototypeOf(Object.prototype)// null`\r\n\r\nundefined表示\"缺少值\"，就是此处应该有一个值，但是还没有定义。\r\n（1）变量被声明了，但没有赋值时，就等于undefined。\r\n（2）调用函数时，应该提供的参数没有提供，该参数等于undefined。\r\n（3）对象没有赋值的属性，该属性的值为undefined。\r\n（4）函数没有返回值时，默认返回undefined。\r\n\r\n`var i;\r\ni // undefined`\r\n`function f(x){console.log(x)}\r\nf() // undefined`\r\n`var  o = new Object();\r\no.p // undefined`\r\n`var x = f();\r\nx // undefined`\r\n"}}
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