Incorporating TypeScript basics into the if statement post compiling

As I delve into the Angular2 Quickstart, I stumbled upon a peculiar issue within app.component.js after compiling app.component.ts using tsc (version 1.8.2):

if (d = decorators[i])

I am unable to pinpoint where I may have gone wrong in configuring the quickstart sample. Any assistance would be greatly appreciated!

This is my code:

app.component.ts

import {Component} from 'angular2/core';


@Component({
    selector: 'my-app',
    templateUrl: '/templates/AppComponent.html'
})
export class AppComponent {
    public name: string = "My test app";
}

package.json

{
  "name": "iSandBox",
  "version": "1.0.0",
  "scripts": {
    "start": "concurrent \"npm run tsc:w\" \"npm run grunt\" \"npm run lite\" ",
    "tsc": "tsc",
    "tsc:w": "tsc -w",
    "lite": "lite-server",
    "typings": "typings",
    "postinstall": "typings install",
    "grunt": "grunt"
  },
  "license": "ISC",
  "dependencies": {
    "angular2": "2.0.0-beta.7",
    "systemjs": "0.19.22",
    "es6-promise": "^3.0.2",
    "es6-shim": "^0.34.4",
    "reflect-metadata": "0.1.3",
    "rxjs": "5.0.0-beta.2",
    "zone.js": "0.5.15"
  },
  "devDependencies": {
    "concurrently": "^2.0.0",
    "grunt": "^1.0.0-rc1",
    "grunt-contrib-copy": "^0.8.2",
    "grunt-contrib-jshint": "~1.0.0",
    "grunt-contrib-nodeunit": "~0.4.1",
    "grunt-contrib-uglify": "~0.11.1",
    "gulp": "^3.9.1",
    "gulp-concat": "^2.6.0",
    "gulp-rename": "^1.2.2",
    "gulp-tslint": "^4.3.2",
    "gulp-uglify": "^1.5.3",
    "gulp-util": "^3.0.7",
    "lite-server": "^2.1.0",
    "typescript": "^1.7.5",
    "typings": "^0.6.8"
  },
  "ambientDependencies": {
    "es6-shim": "github:DefinitelyTyped/DefinitelyTyped/es6-shim/es6-shim.d.ts#6697d6f7dadbf5773cb40ecda35a76027e0783b2"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "es5",
    "module": "system",
    "moduleResolution": "node",
    "sourceMap": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "removeComments": false,
    "noImplicitAny": false
  },
  "exclude": [
    "node_modules",
    "typings/main",
    "typings/main.d.ts"
  ]
}

app.component.js

System.register([ 'angular2/core' ],
    function(exports_1, context_1) {
        "use strict";
        var __moduleName = context_1 && context_1.id;
        var __decorate = (this && this.__decorate)
                || function(decorators, target, key, desc) {
                    var c = arguments.length, r = c < 3 ? target
                            : desc === null ? desc = Object
                                    .getOwnPropertyDescriptor(target, key) : desc, d;
                    if (typeof Reflect === "object" && typeof Reflect.decorate === "function")
                        r = Reflect.decorate(decorators, target, key, desc);
                    else
                        for (var i = decorators.length - 1; i >= 0; i--)
/*=================HERE===>>>>*/  if (d = decorators[i])
                                r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
                    return
                            c > 3 && r && Object.defineProperty(target, key, r), r;
                };
        var core_1;
        var AppComponent;
        return {
            setters : [ function(core_1_1) { core_1 = core_1_1; } ],
            execute : function() {
                AppComponent = (function() {
                    function AppComponent() {
                        this.name = "My test app";
                    }
                    AppComponent = __decorate(
                            [core_1.Component({
                                        selector : 'my-app',
                                        templateUrl : '/templates/AppComponent.html'
                                    }),
                            __metadata('design:paramtypes',[]) ], AppComponent);
                    return AppComponent;
                }());
                exports_1("AppComponent", AppComponent);
            }
        }
    });
// # sourceMappingURL=app.component.js.map
javascripttypescriptangular

Answer №1

Performing an assignment within a test does not necessarily imply error. For example:

if (d = decorators[i])

is equivalent to:

d = decorators[i];
if (d)

Let's analyze the entire if statement:

if (d = decorators[i])
    r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;

It can be observed that the body of the if statement is using d as a function, hence the condition serves as a guard to avoid calling something falsy (which is not a function).

This code essentially iterates through each element in decorators, invoking non-falsy ones as functions.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Avoiding Socket IO from timing out when the browser page is inactive or not the focused tab on Google Chrome, Mozilla Firefox, and Safari mobile browsers

I have developed a basic chat application using socket io. The functionality is quite similar to the socket io chat official demo. However, I am facing an issue where Socket io times out on all mobile browsers when the user minimizes the page, opens anothe ...

javascriptnode.jsgoogle-chromesocket.iosettimeout

Posting data using the form method="post" in Vue does not seem to be working

My goal is to create a website that allows users to reserve a seat using a specific password and time slot. I've set up a form where users can input the password and their name, then submit the form to make the reservation. However, I'm facing an ...

javascripthtmlvue.js

Is there a way to trigger a function with the onclick event in NextJs?

Working on my NestJS project, I am still a beginner in the field. My current task involves creating a web application that displays a leaflet map with clickable tiles. Each tile should have a button that triggers a specific function when clicked. However, ...

javascriptfunctionnext.jsleafletreact-leaflet

How to troubleshoot passing json data from a controller to an AngularJS directive

I recently started learning AngularJS and I'm facing an issue with passing JSON data from the controller to a directive. When I try to display the data, nothing shows up and I encounter the following errors: 1. Uncaught SyntaxError: Unexpected token ...

javascriptangularjs

Can an attribute be assigned to an Angular host element without specifying a value?

Exploring the concept of host binding on the input element's readonly attribute, aiming to add the attribute without assigning any value. Even though HTML specifications state that assigning a value may not make a difference as long as the attribute i ...

angulartypescript

Turning a stateful React component into a stateless functional component: Ways to achieve functionality similar to "componentDidMount"

I recently developed a small, stateful React component that utilizes Kendo UI to display its content in a popup window when it loads. Here is a snippet of the code: export class ErrorDialog extends React.Component { constructor(props, context) { sup ...

javascriptdomreactjsevent-handlingwindow-load

using a function as an argument in the map method within a React component

I have a challenge where I am trying to display blog posts retrieved from my database. However, for each item, I also need to execute a download image function. I attempted to include the function within the .map function but encountered some errors. I am ...

javascriptreactjsnext.js

How is it that cross-domain scripting is able to occur with local files on a smartphone or tablet?

My Experiment: To test cross-site scripting (XSS), I set up an index.html file with a xss.js script that utilized the jQuery.get() function. After opening the index.html in various browsers (Firefox, Chrome, IE, and Opera), I attempted to trigger an ajax ...

javascriptandroidajaxmobilecross-domain

The convention for naming the StoreModule.forRoot in ngrx

So in my Angular Application's app.module.ts file, I have the following setup: StoreModule.forRoot({ applicationState: applicationReducer, }), In my app.reducer.ts file, I have defined the initial state and a movies reducer like this: export const ...

angularngrxstore

The filtering process of an array using the filter() method is effective, however, it does not result in any visible changes on

script.js searchVideo = (keyword) => { this.input = keyword; if(this.items.length == 0){ this.filteredItems = []; } if(!this.input){ this.filteredItems = this.items; } const args = this ...

angularangular5angular7angular8angular9

C# web service is unable to return a specific value

I attempted to use a basic web service (just to test if the value will populate in the JavaScript code). I experimented with a very simple snippet, but it kept returning 'undefined'. Can you offer some guidance? I have tried several solutions wit ...

javascriptc#ajax

Deactivating a Vue custom filter when hovering over it

I'm trying to figure out how to disable a truncate filter when hovering over an element using VueJS 2. Here's the part of my template that includes the filter: <div class="eng" @mouseover="showAll">{{ word.english | truncate }}</div> ...

javascripteventsevent-handlingvue.jsvuejs2

Is it possible to transmit fixed routing information utilizing a path that can be customized with parameters?

Within my route definition, I am passing static data like this: const routes: Routes = [{ path: '/map', component: MapComponent, data: { animation: 'mapPage' } }]; To access this data ...

angularangular2-routing

Angular Pipe displays values properly, but ngFor fails to render them

I am using a pipe to filter my ngFor loop with exact matches that are passed through by clicking on the filter argument. Below is the code for my pipe: transform(values: any[], criteria: string, group): any[] { if (!values) { ...

angulartypescriptngforangular-pipe

Tips for customizing the background color of the MUI Menu Popover within a TextField that has the select property

In my quest to customize the appearance of a popover or menu in a TextField with the 'select' property, I referred to MUI customization docs for guidance. Successfully changing the text and label color of a TextField using the code below: const u ...

javascriptreactjsmaterial-ui

Enhancing React components with dynamic background colors for unique elements

I am encountering an issue while using a map in my code. Specifically, I want to set the background of a particular element within the map. The element I am referring to is "item .title". I aim for this element to have a background color like this: https:/ ...

javascriptcssreactjsreduxreact-redux

Troubleshooting Angular2: Issues with ngModel functionality within an ngIf directive

Whenever I attempt to reference an NgModel directive using a template reference variable within an *ngIf statement, I encounter a "Cannot read property 'valid' of undefined" error. Consider the following form as an example: <form (ngSubmit)= ...

angularangular2-formsangular2-directives

Getting the click event object data from a dynamically created button with jQuery or JavaScript

I have a task of tracking page button click events. Typically, I track the objects from statically created DOM elements using: $('input[type=button]').each(function () { $(this).bind('click', function () { ...

javascriptjqueryjquery-events

Struggling to pass command line arguments to index.ts with yarn?

My objective is to pass arguments through the command line using yarn start to index.ts. "scripts": { "start": "tsc-watch --onSuccess \"ts-node --pretty -r tsconfig-paths/register' src/index.ts\"", } When I attempt something like: yarn ...

javascriptnpmyarnpkg

Synchronize numerous PouchDB databases with a single CouchDB database

After reading the PouchDB documentation, I learned that sync occurs between a local database and a remote CouchDB database. Currently, I am working on developing a native application that includes a unique local database for each user (multiple databases) ...

javascriptnode.jsnosqlcouchdbpouchdb