Can we pass variables by reference in JavaScript Function?

Question

I am calculating row and column of a given point by javascript function.
To achieve this I have to declare global variables

var global_row;
var global_col;

Here is function body

function calculate_city_row_col(cur_city_id)
{
    var r = 565;
    var c = 1;
    var max_city_id = 159895;
    do{
        if((r%2) == 0) c++;
        max_city_id -= r;
        r--;
    }
    while(cur_city_id <= max_city_id)

    //Saving Result in seperate row and column
    global_row = r + 1;                                 //Global Variable
    global_col = c + (cur_city_id - (max_city_id + 1)); //Global Variable
}

Here is function call

var city_id = 1244;
calculate_city_row_col(city_id);
var city_row = global_row;
var city_col = global_col;

Is there anyway to directly pass local variables? (without using global variables)
like this

calculate_city_row_col(cur_city_id, city_row_ref, city_col_ref);

Esailija · Accepted Answer · 2015-03-22 13:39:50Z

2

Just return an object:

function calculate_city_row_col(cur_city_id)
{
    var r = 565;
    var c = 1;
    var max_city_id = 159895;
    do{
        if((r%2) == 0) c++;
        max_city_id -= r;
        r--;
    }
    while(cur_city_id <= max_city_id)

    return {
        row: r + 1,
        col: c + (cur_city_id - (max_city_id + 1))
    };
}

var rowAndCol = calculate_city_row_col(1244);
var city_row = rowAndCol.row;
var city_col = rowAndCol.col;

answered Mar 22, 2015 at 13:39

Esailija

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Comments

T.J. Crowder · Accepted Answer · 2015-03-22 13:49:18Z

Can we pass variables by reference in JavaScript Function

No. JavaScript is purely pass-by-value (the value passed when you pass an object around is an object reference, but it's still a value).

Your options are:

Have the function return an object (or array)

function calculate_city_row_col(cur_city_id)
{
    var r = 565;
    var c = 1;
    var max_city_id = 159895;
    do{
        if((r%2) == 0) c++;
        max_city_id -= r;
        r--;
    }
    while(cur_city_id <= max_city_id)

    //Saving Result in seperate row and column
    return {
        row: r + 1,
        col: c + (cur_city_id - (max_city_id + 1))
    };
}

Usage:

var result = calculate_city_row_col(someCityId);
console.log(result.row);
console.log(result.col);

Have the function accept a reference to an object (or array) that it updates

function calculate_city_row_col(cur_city_id, result)
{
    var r = 565;
    var c = 1;
    var max_city_id = 159895;
    do{
        if((r%2) == 0) c++;
        max_city_id -= r;
        r--;
    }
    while(cur_city_id <= max_city_id)

    //Saving Result in seperate row and column
    result.row = r + 1;
    result.col = c + (cur_city_id - (max_city_id + 1));
}

Usage:

var result = {};
calculate_city_row_col(someCityId);
console.log(result.row);
console.log(result.col);

Barring a strong reason to go with #2 in a specific situation, #1 is usually the best option. For instance, if you were calling this function thousands of times in a tight loop, there might be a justification for reusing a single object (by passing it in) instead of creating a new object every time.

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