Como posso criar dinamicamente o array JavaScript (formato JSON)?

Estou a tentar criar o seguinte: 
var employees = {"accounting": [   // accounting is an array in employees.
                    { "firstName" : "John",  // First element
                      "lastName"  : "Doe",
                      "age"       : 23 },

                    { "firstName" : "Mary",  // Second Element
                      "lastName"  : "Smith",
                      "age"       : 32 }
                  ] // End "accounting" array.                                  

    } // End Employees

comecei com 

 var employees = new Array();

como continuo a criar o array dinamicamente (pode mudar firstName com variável)? Parece que não percebi bem a matriz aninhada.

Author: dakab, 2010-02-12
Source

4 answers

A nossa matriz de objectos 
var someData = [
   {firstName: "Max", lastName: "Mustermann", age: 40},
   {firstName: "Hagbard", lastName: "Celine", age: 44},
   {firstName: "Karl", lastName: "Koch", age: 42},
];

Com for...in 

var employees = {
    accounting: []
};

for(var i in someData) {    

    var item = someData[i];   

    employees.accounting.push({ 
        "firstName" : item.firstName,
        "lastName"  : item.lastName,
        "age"       : item.age 
    });
}

Ou com Array.prototype.map(), o que é muito mais limpo: 

var employees = {
    accounting: []
};

someData.map(function(item) {        
   employees.accounting.push({ 
        "firstName" : item.firstName,
        "lastName"  : item.lastName,
        "age"       : item.age 
    });
}
 218
Author: Alex, 2018-01-04 15:38:12 
var accounting = [];
var employees = {};

for(var i in someData) {

    var item = someData[i];

   accounting.push({ 
        "firstName" : item.firstName,
        "lastName"  : item.lastName,
        "age"       : item.age 
    });
}

employees.accounting = accounting;
 31
Author: Chase, 2014-03-21 21:07:30

O Que eu faço é algo um pouco diferente da resposta @ Chase: 

var employees = {};

// ...and then:
employees.accounting = new Array();

for (var i = 0; i < someArray.length; i++) {
    var temp_item = someArray[i];

    // Maybe, here make something like:
    // temp_item.name = 'some value'

    employees.accounting.push({
        "firstName" : temp_item.firstName,
        "lastName"  : temp_item.lastName,
        "age"       : temp_item.age
    });
}
E esse trabalho formem-me! Espero que possa ser útil para outro corpo!
 4
Author: Alex Ventura, 2016-06-19 21:28:11 
var student = [];
var obj = {
    'first_name': name,
    'last_name': name,
    'age': age,
}
student.push(obj);
 2
Author: Venu Upadhyay, 2017-06-24 18:24:56