object-provide

Install

npm install object-provide

Intro

This single function library represents a common pattern.

Adding behavior conditionally.

A Simple Example

var extend = require('object-provide'),
    //Extend with the first call to extend.
    firstExtension = true;

function AConstructor(){}

//This assignment succeeds.
extend(AConstructor.prototype, firstExtension, {
    aMethod: function(){
        console.log('I am the first one.')
    }
});

//This assignment does not succeed.
extend(AConstructor.prototype, !firstExtension, {
    aMethod: function(){
        console.log('I am the second one.')
    }
});

The alternative could be.

var firstExtension = true;
function AConstructor(){}

if(firstExtension){
    AConstructor.prototype.aMethod = function(){
        console.log('I am the first one.')
    };
}else{
    AConstructor.prototype.aMethod = function(){
        console.log('I am the second one.')
    };
}

The Interface

extend(destination, use|source, source|filter)

destination is the object you want to extend with the source object.

use is a boolean. When use is true source properties are assigned to destination.

filter is a function callback.

filter(destination, source, value, key) -> boolean

The filter callback is used as a final control of properties. This filter callback is actually both a forEach, and a filter.

The value is the current property value of the source object.

key is the current property key of the source object.

When the return value is false the current property is not set.

When the return value is true, or undefined the current property is set.

Additionally you can set the value inside of the filter callback. Just return false if you do.

Usage of filter

extend(AConstructor.prototype, firstExtension, {
    aProp: "Don't use me",
    aMethod: function(){
        console.log('I am the first one.')
    }
}, filter);

//For some odd reason we don't use "aProp" because it contains a string..
function filter(dest, source, value, key){
    if(typeof key === 'aProp' && typeof value === 'string'){
        return false;
    }
}

A more pragmatic example

extend(Array.prototype, Array.prototype.includes ? true : false, {
    includes: function(searchElement /*, fromIndex*/ ) {
        'use strict';
        var O = Object(this);
        var len = parseInt(O.length) || 0;
        if (len === 0) {
            return false;
        }
        var n = parseInt(arguments[1]) || 0;
        var k;
        if (n >= 0) {
            k = n;
        } else {
            k = len + n;
            if (k < 0) {k = 0;}
        }
        var currentElement;
        while (k < len) {
            currentElement = O[k];
            if (searchElement === currentElement ||
                 (searchElement !== searchElement && currentElement !== currentElement)) { // NaN !== NaN
                return true;
            }
            k++;
        }
        return false;
    }
});

About

The Array.prototype.includes polyfill example is contrived.

This library is better used as a library helper. Where you add the behavior you want based on some condition that can't be controlled by the developer at run time.

So when you release a library it goes out, and acts exactly as it should. That is if you've taken the proper measures to make the alternative behaviors act the same. Which I know is a contradiction, but I think you know what I mean. :)

For instance let's say you have a library that has it's own includes.

var canIncludes = Array.prototype.includes ? true : false;

function MyLib(){}

extend(MyLib.prototype, canIncludes, {
    includes: function(){
        return Array.prototype.includes.apply(this, arguments);
    }
});

extend(MyLib.prototype, !canIncludes, {
    includes: function(){
        //The alternate behavior.
    }
});

This conditional behavior can be used to set multiple properties as well.

Overall it is easy to just use ifelse branches to set properties conditionally, but object-provide is the implementation of this common idiom. Maybe code using object-provide can be slightly more organized, and provide good visual markers in code where conditional properties exist. Also don't repeat yourself though it could be argued there really isn't any less characters than using ifelse.

Maybe if you assign object-provide to just one, or two characters then you have less code:

var OP = require('object-provide');

Happy coding!