JavaScript数组转json（可以降低一级时间复杂度）

let arr2json = (arr,propertyname)=>arr.reduce((total,next)=>Object.assign(total,{[next[propertyname]]:next}),{})

let arr = [
    {name:"北京",age:100},
    {name:"上海",age:99},
    {name:"深圳",age:98},
    {name:"广州",age:97},
    {name:"重庆",age:96},
    {name:"苏州",age:95},
    {name:"成都",age:94},
    {name:"武汉",age:93},
    {name:"杭州",age:92}
]

let arr2json = (arr,propertyname)=>arr.reduce((total,next)=>Object.assign(total,{[next[propertyname]]:next}),{})

console.log(arr2json(arr,'name'))

输出为： 

{ '北京': { name: '北京', age: 100 },
  '上海': { name: '上海', age: 99 },
  '深圳': { name: '深圳', age: 98 },
  '广州': { name: '广州', age: 97 },
  '重庆': { name: '重庆', age: 96 },
  '苏州': { name: '苏州', age: 95 },
  '成都': { name: '成都', age: 94 },
  '武汉': { name: '武汉', age: 93 },
  '杭州': { name: '杭州', age: 92 } }