Extending sffjs.md

Extending sffjs

Let's say you have a class called Person that you want to format using sffjs.

function Person(firstname, lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
}

Trying to format a Person won't provide any useful string:

var person = new Person("John", "Doe");

String.format("Hello {0}!", person);
// output:
// "Hello [object Object]!"

Implement toString

The first step is to override toString on the Person class. sffjs will then use your toString implementation.

function Person(firstname, lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
}
Person.prototype.toString = function Person_toString() {
    return this.firstname + " " + this.lastname;
};

var person = new Person("John", "Doe");

String.format("Hello {0}!", person);
// output:
// "Hello John Doe!"

Much better!

Implement __Format

You can also provide a formatter accepting a format string. In this case, you should define a method called __Format on your class.

function Person(firstname, lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
}
Person.prototype.__Format = function Person_Format(formatString) {
    switch (formatString) {
        case "F": return this.firstname;
        case "L": return this.lastname;
    }
    return this.firstname + " " + this.lastname;
};

var person = new Person("John", "Doe");

String.format("Hello Mr {0:L}!", person);
// output:
// "Hello Mr Doe!"

If you have defined both __Format and toString, __Format will have precedence.

Sffjs will extend the builtin datatypes Number and Date with a __Format method.