format strings like python3

format.js

function format() {
    var args, fmt, result;
    
    args = Array.prototype.slice.apply(arguments);
    fmt = this instanceof String ? this : args.shift();
    
    if (args.length === 1 && typeof args[0] === "object") {
        args = args[0];
    }

    result = fmt.replace(/{([^}]+)}/g, function (s, id) {
        var chain = id.split("."), substr, i;

        if (chain.length >= 2) {
            substr = args[chain[0]];
            for (i = 1; i < chain.length; i++) {
                substr = substr[chain[i]];
            }
        } else {
            substr = args[id];
        }
        return substr;
    });

    return result;
}

//String.prototype.format = format;

/*Usage:
format("pi is {0}", Math.PI);
//"pi is 3.141592653589793"
format("pi is {PI}, sqrt2 is {SQRT2}", Math);
//"pi is 3.141592653589793, sqrt2 is 1.4142135623730951"
format("pi is {0.PI}, max value is {1.MAX_VALUE}", Math, Number);
//"pi is 3.141592653589793, max value is 1.7976931348623157e+308"
format("fruits {0}, {1}, {0}!", ["apple", "lemon", "oranges"]);
//"fruits apple, lemon, apple!"
*/