Why did forEach only run out of the first value? There's no way to print it all.

suppose there is a group leader like this 

 var qq = [
  
  {
    "info": {"event": 123},
    "odds": 
    [
      {"o": ["test","123",],
        "oName": " "
      },
      {"o": ["qq","ee",],
        "oName": ""
      },
    ],
    "main": true,
  },
  {
    "info": {"event": 323},
    "odds": [
      {"o": ["jk","234"] ,
        "oName": ""
      }
    ],
    "main": true,
  }
  ];

I want to print out every oName 

qq.forEach(function(item,i){
  
    console.log(item.odds.oName)
    //undefined
    
    console.log(item.odds[i].oName)
    //" "
    //"TypeError: Cannot read property "oName" of undefined

  return

});

Why is it impossible to print out all the oName? How to solve it?

Javascript
Apr.13,2022
dude, how about the for loop 
          
           for(var i=0;i<qq.length;iPP){
                for(var j=0;j<qq[i].odds.length;jPP){
                console.log(qq[i].odds[j].oName);
                }
            }

clipboard.png 

qq.forEach(item => {
  item.odds.forEach(val => { // oddsforEach
    console.log(val.oName)
  })
})

this certainly won't work. Odds is also an array, and the simplest and roughest thing is a double loop: 

qq.forEach((item,i)=>{
    if (item.odds) {
        item.odds.forEach((val,index)=>{
            console.log(val.oName)
        })
    }
});
  1. "odds" is an array console.log (item.odds.oName) it must be undefined Ah

2. 

qq.forEach((item) => {  
      item.odds.forEach((childItem) => {
         console.log(childItem.oName) 
      })
});



qq.forEach(function(item) {
    if (item.odds.length > 0) {
        item.odds.forEach(function(items, index) {
            console.log(items.oName)
        })
    }
})

forEach traverses only one layer, while the oName attribute belongs to the second layer
qq.forEach ((item) = > {

) 
item.adds.map((val)=>{
    console.log(val.oName)
})

})

first of all, you can see that this is an error code. When the array executes to the second loop, there will be a undefined error:

  • first loop: item exists, item0; you can output item.odds [I] .oName; that is, the oName; of the first element of item.odds is correct.
  • second loop: item exists, iDiver1; you can output item.odds [1] .oName; that is, the oName; of the second element of item.odds, but item.odds has only one element, so a undefined error occurs.

there is a return in your forEach, which means that if you loop once, you will return, instead of looping

qq.forEach (function (item) {

) 
if (item.odds.length > 0) {
    item.odds.forEach(function(items, index) {
        console.log(items.oName)
    })
}

})

Previous: Error during startup of spring boot 2.0.x external tomcat

Next: When does vuex use action and when does state (update or get) be used?

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3ae74-2c256.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3ae74-2c256.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?