defaultify

utility javascript module to set object literals used as options for functions

Used to setup option objects with default values.

Overwrite default values with user-given values

You have a function taking an object with the possible keys minValue (defaulting to 1) and maxValue (defaulting to 5). The default value are {minValue: 1, maxValue: 5}

// the user overwrites minValue, but uses the default value for maxValue
doStuff({
    minValue: 2
});

// doStuff should use the following object as options
{
    minValue: 2,
    maxValue: 5
}

// doStuff could accomplish this with:
function doStuff(options) {
    var defualtOpts = {
        minValue: 1,
        maxValue: 5
    };
    // opts is an object with the keys info (details about the change) and value (the options to use)
    var opts = defaultify(options, defualtOpts);
    opts = opts.value;
    
    // shorter, raising error if the user passes illigal options
    // var opts = defaultify(options, defualtOpts, true).value;
    
    ...

}

Transform user given values

You have a function taking a command (string) as one of the object values. But you want abbreviations to be allowed

// user uses abbreviation for test
doCommand({command: "t"});

// doCommand can use a transform function to change this type
function doCommand(options) {
    var defualtOpts = {
        command: "run"
    };
    var transform = {
        command: function(value) {
            // value is the value passed in by the user, in this case "t"
            if (value === "r") return "run";
            if (value === "t") return "test";
            return value;
        }
    };
    var opts = defaultify(options, defualtOpts, transform, true).value;
    
    ...
}

Transform functions as validators

Transform functions can also be used to validate user input. In the example above, the transform object can be changed to

var transform = {
    command: function(value) {
        if (value === "r" || value === "run") return "run";
        if (value === "t" || value === "test") return "test";
        throw new Error("Invalid command '" + value + "'");
    }
};

// calling doCommand with an invalid command text raises an error
try {
    doStuff({command: "say hello"});
} catch (e) {
    // e.message === "transform failed: Invalid command 'say hello' for command"
}