Question

I have a javascript object that goes like this:

var obj = {"data":
 [
  {"name":"Alan","height":1.71,"weight":66},
  {"name":"Ben","height":1.82,"weight":90},
  {"name":"Chris","height":1.63,"weight":71}
 ]
 ,"school":"Dover Secondary"
}

How do I create a new field called BMI using weight/(height)^2 such that the new object becomes:

var new_obj = {"data":
 [
  {"name":"Alan","height":1.71,"weight":66,"BMI":22.6},
  {"name":"Ben","height":1.82,"weight":90,"BMI":27.2},
  {"name":"Chris","height":1.63,"weight":71,"BMI":26.7}
 ]
 ,"school":"Dover Secondary"
}

Answer 1

var persons = obj.data;
var new_obj = {data: [], school: obj.school};
for(var i=0; i<persons.length; i++){
    var person = persons[i];
    new_obj.data.push({
        name: person.name,
        height: person.height,
        weight: person.weight,
        BMI: Math.round(person.weight / Math.pow(person.height, 2)*10)/10;
    });
    /* Use the next line if you don't want to create a new object,
       but extend the current object:*/
    //persons.BMI = Math.round(person.weight / Math.pow(person.height, 2)*10)/10;
}

After new_obj is initialised, a loop walks through array obj.data. The BMI is calculated, and added along with a copy of all properties to new_obj. If you don’t have to copy the object, have a look at the commented part of the code.