jquery ajax無法獲取回調(diào)json ,并且報(bào)parsererror錯(cuò)誤

各種百度說這個(gè)錯(cuò)誤是因?yàn)閖son格式不標(biāo)注引起的

這是后端php 用json_encode函數(shù)生成的json

看了jquery的官方文檔似乎沒錯(cuò)
jQuery.parseJSON( json )
Passing in a malformed JSON string will result in an exception being thrown. For example, the following are all malformed JSON strings:

{test: 1} (test does not have double quotes around it). 譯：test兩邊必須有雙引號(hào) {"test":1}
{'test': 1} ('test' is using single quotes instead of double quotes). 譯：test兩邊的引號(hào)不能為單引號(hào)，一定要是雙引號(hào)
Additionally if you pass in nothing, an empty string, null, or undefined, 'null' will be returned from parseJSON. Where the browser provides a native implementation of JSON.parse, jQuery uses it to parse the string. For details on the JSON format, see http://json.org/.

而且以前一直都是這么返回的都沒有出錯(cuò)，請(qǐng)問那么正確的json標(biāo)準(zhǔn)格式應(yīng)該是怎樣的？