How to use js to parse the database (with code)

This time I will show you how to use js to parse the database (with code), and what are the precautions for using js to parse the database. The following is a practical case, let's take a look.

TypeError: Cannot read property 'xxx' of undefined
TypeError: Cannot read property 'xxx' of null
TypeError: xxx.map is not a function

These anomalies are difficult to detect, and they may not be discovered even if they are posted online in time. Because these problems are caused by data anomalies. What if we elegantly solve or avoid these problems that affect the user experience?

// 第一种做法肯定是这样的
if(a){
  return a.name || '你没名字'
}
// 这种做法处理简单的还能凑合用，但是如果你遇到这样的呢 user.country.area.city.name,难道要这样写
if(user && user.country && user.country.area && user.country.area.city){
  return user.country.area.city.name || '你没名字'
}
// 这是多么痛苦的一件事情 @后端兄弟
// 第二种，感谢es6
let {country={area:{city:{name:'你没名字'}}}} = user;
这个感觉也不是很好的解决方案
// 第三种，利用reduce构建一个解析函数
function getValue(obj,key){
  return key.split('.').reduce(function(o,k){
    // o,当前对象
    // key，数组下一个元素
    if((typeof o === 'undefined' || o === null)){
      return k.indexOf('[array]') !== -1?[]:o
    }else{
      return k.indexOf('[array]') !== -1?(o[k.replace('[array]','')]||[]):o[k]
    }
  },obj)
}
let user1;
let user2 = {
 
}
let user3 = {
 country:{
  area:{
   city:{
    name:'12312'
   }
  }
 }
}
let user4 = {
 country:[
  {
   city:{
    name:'12312'
   }
  }
 ]
}
let user5 = {
 country:{
  city:[1,2,3]
 }
}
console.log(getValue(user1,'country.area.city.name'))
console.log(getValue(user2,'country.area.city.name'))
console.log(getValue(user3,'country.area.city.name'))
console.log(getValue(user5,'country.city[array]'))
console.log(getValue(user5,'country.city[array].1'))
console.log(getValue(user5,'country.city[array].10'))
console.log(getValue(user5,'country.city[array].1.name'))
console.log(getValue(user5,'country.city[array].persion[array]'))
// 输出结果
undefined
undefined
"12312"
[1, 2, 3]
2
undefined
undefined
[]

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Recommended reading:

JS encapsulation fade-in and fade-out function function

webpack.config.js parameter usage tutorial

The above is the detailed content of How to use js to parse the database (with code). For more information, please follow other related articles on the PHP Chinese website!