[{"cityname":"value"},"price":"100"]

你返回的数据大概长这样，如果去掉你说的那个单引号就长这样

[{"cityname":value},"price":"100"]

看字符串拼接要一截一截看，从开头那个最外层的引号，看到第一个对应的引号

'{"cityname":"' //第一截去掉单引号：{"cityname":" 
.$cities[$i].//第二截这个是变量：武汉
'","price":"'//第三截:  ","price":"
.rand(500,1500).//第四截：501
'"}]';//第五截： "}]

//把上面解析出来的拼起来
{"cityname":"武汉","price":"501"}]