Assume that I need a JavaScript dictionary (object/ associative array) which I need to access as follows:

var value = dict[foo][bar][buz][qux]; // this could go on

Which is the best way to initialize this dictionary? The only way I can think of is:

// 'foo', 'bar', 'baz', 'qux' are variables
var dict = {};
dict[foo] = {};
dict[foo][bar] = {};
dict[foo][bar][buz] = {};
dict[foo][bar][buz][qux] = value;

Alternatively, is there a better way of achieving the same results? I would prefer a solution that works both in browsers and Node.js.

Assume that I need a JavaScript dictionary (object/ associative array) which I need to access as follows:

var value = dict[foo][bar][buz][qux]; // this could go on

Which is the best way to initialize this dictionary? The only way I can think of is:

// 'foo', 'bar', 'baz', 'qux' are variables
var dict = {};
dict[foo] = {};
dict[foo][bar] = {};
dict[foo][bar][buz] = {};
dict[foo][bar][buz][qux] = value;

Alternatively, is there a better way of achieving the same results? I would prefer a solution that works both in browsers and Node.js.

• javascript
• object
• dictionary
• initialization
• associative-array

3 Answers 3

An option is to build the object dynamically, like:

var vals = [1, 2, 3, 4];

function createObject(arr) {
    var obj = {};
    var mod = obj;
    for (var i = 0, j = arr.length; i < j; i++) {
        if (i === (j - 1)) {
            mod.value = arr[i];
        } else {
            mod[arr[i]] = {};
            mod = mod[arr[i]];
        }
    }
    return obj;
}

console.log(createObject(vals));

DEMO: http://jsfiddle/BnkPz/

So your list of variables would have to be put into an array and passed to the function, or the function could modified to work with any number of passed arguments.

Use JSON.parse:

var dict = JSON.parse('{ "' + foo + '": { "' + bar + '": { "' + buz + '": { "' + qux + '": "value"}}}}');

You could create a function that takes the object to modify, a path to the leaf property (a dot-delimited string like foo + '.' + bar + '.' + buz + '.' + qux), and the value, and let it loop and do the job for you:

var foo = 'foo',
    bar = 'bar',
    buz = 'buz',
    qux = 'qux',
    path = foo + '.' + bar + '.' + buz + '.' + qux,
    dict = {};

createNestedProperty(dict, path, 10);
console.log(dict);

function createNestedProperty(dict, path, value) {
    var pathArray = path.split('.'),
        current;
    while(pathArray.length) {
        current = pathArray.shift();
        if(!dict.hasOwnProperty(current)) {
            if(pathArray.length) {
                dict[current] = {};  
            // last item
            } else {
                dict[current] = value;     
            }
        }
    }
}

http://jsfiddle/NuqtM/

Also, a similar question was asked here: Extend a JavaScript object by passing a string with the path and a value.