如何在没有特定键的情况下从JSON对象获取值

Question

I have below JSON object from which I want to fetch only certain values on my dev console log using javascript. I tried but below code but I don't know how to loop through array of array. Can anyone please suggest how can i achieve this.

var infoJSON;
for(key in myClass) {
  infoJSON = myClass[key];
  console.log(infoJSON);
}




var myClass= {
   "Subjects":"3",
   "Subject":{
      "maths":{
         "subject_id":"1",
         "subject_level":"easy",
         "marks":"90"
      },
      "english":{
         "subject_id":"2",
         "subject_level":"medium",
         "marks":"80"
      },
      "physics":{
         "subject_id":"3",
         "subject_level":"tough",
         "marks":"70"
      }
   },
   "Average": "80"
};

I am trying to write JavaScript function that outputs the total number of subjects, each subject with marks, and average marks in the browser dev tools console in format given below.

Subjects: 3
- maths (90)
- english (80)
- physics (70)
Average: 80

The code should work for ANY JSON object with the same structure so don't want to use hard coded keys (eg. maths,physics)

Answer 1

This can be done using simple for in , Object.keys() .

Try the following:

 var myClass= {"Subjects":"3","Subject":{"maths":{"subject_id":"1","subject_level":"easy","marks":"90"},"english":{"subject_id":"2","subject_level":"medium","marks":"80"},"physics":{"subject_id":"3","subject_level":"tough","marks":"70"}},"Average":"80"}; for(key in myClass){ if(myClass[key].constructor.toString().indexOf("Object") > 0){ Object.keys(myClass[key]).forEach((k)=>{ console.log(k +" - "+ myClass[key][k].marks); }); } else{ console.log(key +" - " +myClass[key]); } } 

Answer 2

It would be just a question of checking what you are iterating in your class. In case the key is a string, you can simply print it, in case it is not, you can iterate it keys, and print that one

 var myClass= {"Subjects":"3","Subject":{"maths":{"subject_id":"1","subject_level":"easy","marks":"90"},"english":{"subject_id":"2","subject_level":"medium","marks":"80"},"physics":{"subject_id":"3","subject_level":"tough","marks":"70"}},"Average":"80"}; for (let key in myClass) { let value = myClass[key]; if (typeof value === 'string') { console.log( `${key}: ${value}` ); continue; } console.log( Object.keys( value ).map( k => `- ${k} (${value[k].marks})` ).join('\\n') ); } // if you want it in one log output console.log( Object.keys( myClass ).reduce( (result, key) => { if (typeof myClass[key] === 'object') { let value = myClass[key]; return result.concat( Object.keys( value ).map( k => `- ${k} (${value[k].marks})` ) ); } result.push( `${key}: ${myClass[key]}` ); return result; }, [] ).join('\\n') ); 

Answer 3

Subjects and Average are always at the same position, so you hardcode it. Then you have to go on the array to determine the other fields:

var myClass= {
   "Subjects":"3",
   "Subject":{
      "maths":{
         "subject_id":"1",
         "subject_level":"easy",
         "marks":"90"
      },
      "english":{
         "subject_id":"2",
         "subject_level":"medium",
         "marks":"80"
      },
      "physics":{
         "subject_id":"3",
         "subject_level":"tough",
         "marks":"70"
      }
   },
   "Average": "80"
};
var infoJSON;
console.log('Subjects: ' + myClass['Subjects']);
for(key in myClass['Subject']) {
  console.log('- ' + key + ' (' + myClass['Subject'][key]['marks'] + ')');
}
console.log('Average: ' + myClass['Average']);