systemjs.config.js in angular2

Question

I am new to angular2 and I want to know the use of all the objects present inside systemjs.config.js file.

System.config({
    paths: {
        // paths serve as alias
        'npm:': 'node_modules/'
    },
    // map tells the System loader where to look for things
    map: {
        // our app is within the app folder
        app: 'dist',
        main: 'main.js',

        // angular bundles
        '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
        '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
        '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
        '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
        '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
        '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
        '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
        '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',

        // other libraries
        'rxjs': 'npm:rxjs',
        'angular-in-memory-web-api': 'npm:angular-in-memory-web-api/bundles/in-memory-web-api.umd.js',
        'primeng':                   'npm:primeng'      
    },
    // packages tells the System loader how to load when no filename and/or no extension
    packages: {
        app: { main: 'main.js', defaultExtension: 'js' },
        api: { defaultExtension: 'js' },
        rxjs: {defaultExtension: 'js'},
        'node_modules/primeng': {
            format: 'cjs',
            defaultExtension: 'js'
          }
         }

});

For example the code pasted above has objects like paths which can be used to specify alias, in the same manner I want to know the use of map and all the inner objects of map, so on.

Answer 1

Well, first of all you tell where the npm package is located, usually at the root, hence:

paths: {
    // paths serve as alias
    'npm:': 'node_modules/'
}

then you give aliases ( shortcut names ) to the packages that you will be using, in this case angular and some 3rd party libs like rxjs, ...

map: {
        // our app is within the app folder
        app: 'dist',
        main: 'main.js',

        // angular bundles
        '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
        '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
        '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
        '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
        '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
        '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
        '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
        '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',

        // other libraries
        'rxjs': 'npm:rxjs',
        'angular-in-memory-web-api': 'npm:angular-in-memory-web-api/bundles/in-memory-web-api.umd.js',
        'primeng':                   'npm:primeng'      
    }

So instead of typing the whole path when you import a library(e.g. 'npm:@angular/core/bundles/core.umd.js'), you will only have to import the alias you gave it ('@angular/core'). When importing the alias, you are sure you're importing the right library.

the 'npm:' in front of the full paths of the libraries, refers to the path 'npm' you initiated above.