Package installer that can handle dependencies.

package-installer.js

/*
  Coded by Jade Allen Cook 2017
  Example Packages -
  [ 
    "KittenService: ", 
    "Leetmeme: Cyberportal", 
    "Cyberportal: Ice", 
    "CamelCaser: KittenService", 
    "Fraudstream: Leetmeme", 
    "Ice: " 
  ]
*/

// cache dom elements
const packageInputElem = document.getElementById('package-input'),
    validatePackagesBtn = document.getElementById('validate-packages-btn'),
    outputElem = document.getElementById('output-data-text');

// validate user packages input
function validatePackages(userPackageArray) {
    // {} to cache packages
    let packages = {};
    // extract package details
    for (let x = 0, max = userPackageArray.length; x < max; x++) {
        // slice/split string to get values
        const packageName = userPackageArray[x].slice(0, userPackageArray[x].indexOf(':')),
            packageDependency = userPackageArray[x].split(':').pop().substr(1);
        // test for duplicate package
        if (packageName in packages) {
            return '<b>Error: </b><br /><br /> ' + packageName + ' was instantiated more than once.';
        }
        // if everything is okay, add to packages {}
        packages[packageName] = packageDependency;
    }
    // test all packages for infinate loops
    const packageNamesArray = Object.keys(packages);
    for (let x = 0, max = packageNamesArray.length; x < max; x++) {
        // cache project details
        const package = packageNamesArray[x];
        let packageDependency = packages[packageNamesArray[x]];
        // only run if there is a dependency
        if (packageDependency) {
            // test for missing dependency
            if (packages[packageDependency] === undefined) {
                return '<b>Error: </b><br /><br /> You forgot to include ' + packageDependency;
            }
            // test if dependencies loop back to package
            let nextPackageDependency = packages[packageDependency];
            do {
                if (package === nextPackageDependency) {
                    return '<b>Error: </b><br /><br /> Rejected because of infinate loop';
                }
                nextPackageDependency = packages[nextPackageDependency];
            } while (nextPackageDependency);
        }
    }
    // expected output if everything is okay
    let validPackagesHTML = '<b>Your Packages: </b><br /><br /><ul>';
    for (let x = 0, max = packageNamesArray.length; x < max; x++) {
        validPackagesHTML += '<li>' + packageNamesArray[x] + '</li>';
    }
    validPackagesHTML += '</ul><br /><b>Everything looks good!</b>';
    return validPackagesHTML;
}

// event listeners 
validatePackagesBtn.addEventListener('click', () => {
    outputElem.innerHTML = validatePackages(JSON.parse(packageInputElem.value));
});

// init package validation
outputElem.innerHTML = validatePackages(JSON.parse(packageInputElem.value));