Update existing variables when in JavaScript array

Question

In JavaScript, when I add variables to an array and then update each element in the array, why does the variable have the same value when output in the console?

In the below I would expect all variables to show 777 in the console but they show 0.

When the array is logged [777,777,777] is shown as expected.

var number1 = 0;
var number2 = 0;
var number3 = 0;

var numbers = [number1, number2, number3];

function updateNumbers() {
  var i;
  for (i = 0; i < numbers.length; i++) {
    numbers[i] = 777;

    console.log(numbers);

    console.log(number1);
    console.log(number2);
    console.log(number3);
  }

}

updateNumbers();

Because number1 and numbers[0] are not the same variable. — VLAZ
– VLAZ, Commented May 9, 2018 at 21:01

Herohtar · Accepted Answer · 2018-05-09 21:39:30Z

2

when you create your array you are passing the variables by value, not a reference to the variable.

var a = 1;
var b = 2;
var c = 3;
var test = [a, b, c];
console.log(test);

you can do what you want (sort of), but you need to use objects.

var a = {
  value: 1
};
var b = {
  value: 2
};
var c = {
  value: 3
};

var test = [a, b, c];
// test[0] refers to a
// test[1] refers to b
// test[2] refers to c

function updateNumbers() {
  var i;
  for (i = 0; i < test.length; i++) {
    test[i].value = 777;
  }
}

updateNumbers();

console.log(test); // this wont output like in your example
console.log(a.value);
console.log(b.value);
console.log(c.value);

edited May 9, 2018 at 21:39

Herohtar

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answered May 9, 2018 at 21:02

NickSlash

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