Javascript pure function example with objects

Question

I have the example below of an impure function. Note the variable a is outside of the function scope is being changed. To get around it, one could clone the object

Answer 1

Change the object:

function transformObject(a) {			
    Object.keys(a).forEach(function (k) { a[k] *= 2; });
}

var a = {
        a : 1,
        b : 2
    };
transformObject(a);		
document.write('
' + JSON.stringify(a, 0, 4) + '
');

Keep the object and return a new object with the result:

function transformObject(a) {
    var b = {};
    Object.keys(a).forEach(function (k) { b[k] = a[k] * 2; });
    return b;
}

var a = {
        a : 1,
        b : 2
    },
    b = transformObject(a);		
document.write('
' + JSON.stringify(a, 0, 4) + '
');
document.write('
' + JSON.stringify(b, 0, 4) + '
');