regex - MessageFormat in javascript (parameters in localized UI strings)

Question

What is a good way for handling parameters in localized strings in javascript? I am using the same format as in java's MessageFormat class, e.g.:

There are {0} apples in basket ID {1}.

Where {0} will be replaced with the first parameter and {1} with the second.

This is the call I want to use in JS (i.e. I want to implement origStr):

var str = replaceParams(origStr, [5, 'AAA']);

I am guessing the best strategy would be to use a regular expression. If so, please offer a good regular expression. But I'm open to hear any other options.

Answer 1

String.prototype.format = function() {
    var args = arguments;

    return this.replace(/{(d+)}/g, function() {
        return args[arguments[1]];
    });
};

// Returns '2 + -1 = 1'.
'{0} + {1} = {2}'.format(2, -1, 1);

Or to fit your requirement:

function replaceParams(string, replacements) {
    return string.replace(/{(d+)}/g, function() {
        return replacements[arguments[1]];
    });

    // Or, if prototype code above...
    String.format.apply(string, replacements);
}

You can add fancy i18n features such as ordinal-i-fying (whatever it's called):

// Not well tested.

i18n.en.filters = {
    ordinal: function(n) {
        // FIXME Doesn't handle all cases.
        switch(('' + n).substr(-1)) {
            case '1':
                return '' + n + 'st';
            case '2':
                return '' + n + 'nd';
            case '3':
                return '' + n + 'rd';
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
            case '0':
                return '' + n + 'th';
            default:
                return n; // Just in case...
        }

    },
    plural: function(n, singular, plural) {
        if(n == 1) {
            return singular;
        } else {
            return plural;
        }
    }
};

i18n.current = i18n.en;

String.prototype.format = function() {
    var args = arguments;

    return this.replace(/{((d+)((|w+(:w+)*)*))}/g, function() {
        var arg = args[arguments[2]],
            filters = arguments[3].split('|'),
            i, curFilter, curFilterArgs, curFilterFunc;

        for(i = 0; i < filters.length; ++i) {
            curFilterArgs = filters[i].split(':');
            curFilter = curFilterArgs.shift();
            curFilterFunc = i18n.current.filters[curFilter];

            if(typeof curFilterFunc === 'function') {
                arg = curFilterFunc.apply(null, [ arg ].concat(curFilterArgs));
            }
        }

        return arg;
    });
};

'You have {0} {0|plural:cow:cows} but I have {1} {1|plural:cow:cows}.'.format(2,1);
'My horse came in {0|ordinal} place while yours came in {1|ordinal}.'.format(42,1);