This implements a stateful function in javascript using closure. The same construct requires either a singleton class or a static variable in other languages.

color_picker.js

var pick_color = (function(str) {
    // We use a circular buffer here to allocate the colors.  `label_color_map`
    // is a hash with key as `str` and value is the index into the `colors`
    // list. The following 'static' variables keep the state within the function.
    var label_color_map = {},
        current_color_idx = 0,
        colors = ['#a6cee3', '#1f78b4', '#b2df8a', '#33a02c', '#fb9a99',
        '#e31a1c', '#fdbf6f', '#ff7f00', '#cab2d6', '#6a3d9a', '#ffff99', '#b15928'];

    return function(str) {
        if (!_.has(label_color_map, str)) {
            current_color_idx = (current_color_idx + 1) % colors.length;
            label_color_map[str] = current_color_idx;
        }
        return colors[label_color_map[str]];
    };
})();