Angular2 access global variables from HTML templat

问题:

I have a global variable to store the list of countries like this:

export var COUNTRY_CODES = ["AD", "AE", "AF" /* and more */];

In one of my component, I'd imported the variable using normal import statement

import { COUNTRY_CODES } from "../constants";

I am able to access this global variable freely in my component code, but failed to achieve something like this on the HTML template:

<option *ngFor="let countryCode of COUNTRY_CODES" [value]="countryCode">{{countryCode | countryName}}</option>

I could just pass along the global variable to component by defining a local variable and assign the global variable to it during initialization.

ngOnInit() {
  this.countryCodes = COUNTRY_CODES;
}

And change the ngFor to loop on this local variable to make it works.

My question: Is this the right way to do? I'm not totally comfortable with defining bridging variables every time I want to use global variables in my template.

回答1:

You are creating a variable countryCodes in you component but the view is accessing COUNTRY_CODES instead*

---

Global identifiers like Array, window, document, class and enum names and global variables can't be accessed directly from within the template.

The scope of the template is the component class instance.

What you can do if you need access to any of these, is to create a getter in your component like

import { COUNTRY_CODES } from "../constants";

@Component(...)  
export class MyComponent {
  get countryCodes() { return COUNTRY_CODES; }
  // or countryCodes = COUNTRY_CODES;
}

then it can be used in the template like

<option *ngFor="let countryCode of countryCodes" [value]="countryCode">{{countryCode | countryName}}</option>

Using a shared service like suggested in the other answers works similar. What's the better approach depends on the concrete use case. Services are easy to mock for unit tests in contrary to global variables.

See also

• Select based on enum in Angular2
• How to bind a list in Angular2?

回答2:

First #

you should note that there is a problem in your COUNTRY_CODES. you have put two double quotes at beginning.

It should be ,

Export var COUNTRY_CODES=["AD","AE","AF"];

Second #

Once you pass const value to this.countryCode, you should use it in ngfor loop like,

*ngFor = "let cc in countryCode" [value]="cc"

OR

If you directly want to use it within HTML, Id suggest to make a sharedService to define global variable.

UPDATE

Other way is you can use provide function and define your constant there in provide function within bootstrap function then inject it into respective component to use it.

Check out that way here,

Working Example

回答3:

change this as

export var COUNTRY_CODES = ["AD", "AE", "AF"];

your code have extra " in your array so you have to remove this first than your code run as smothly

working plunker

回答4:

I wanted todo a similar thing, but with a lot of single constants.

Defining a getter for every single one was really annoying - as was the methode of creating a service for these constants, as it meant i could only use them where i can actually inject it ( or again additional work ).

I found that using inline templates, fixed it for me - as it allows to compile the constants into the template - using typescripts multiline `${variable}` template syntax - only thing to look out is that the values have to be wrapped according to their type. Becouse the array.toString() methode would result in '1,2,3,4' so you need to wrap it in "[]"/"'string'" so angular-templating engine picks it up as an array/string again.

Edit: I just saw there was a similar methode mentioned, but i also don't want to inject every single value into the constuctor, as that would be as uncomfortable as defining a member per value.

constants.ts:

export const TEST_STRING = 'route';
export const TEST_ARRAY = [1, 2, 3, 4];

component.ts:

 import {
  TEST_STRING,
  TEST_ARRAY
 } from 'constants.ts'
 @Component({
  selector: 'hn-header',
  template: '
      <a [routerLink]="['${TEST_STRING}']">Link</a>
      <div *ngFor="let test of [${TEST_ARRAY}];">{{test}}</div>
  '
  styleUrls: ['./header.component.css']
 })
 export class HeaderComponent {...}

results in:

<a href="route">Link</a>
<div>1</div>
<div>2</div>
<div>3</div>
<div>4</div>