How to Include JS file in ionic 3

To expand on misha130's answer. You would need to import it into the file you want like this:

import * as test from '../assets/data/test'

This way you have access to the test variable.

console.log(test.testvar);

This solution only worked for me

Put the import js in src/index.html header tag, before the build/polyfills.js and build/main.js (they are in body tag);

Example : I created a file src/assets/test.js with a var testvar, imported in src/index.html and then in src/app/app.component.ts declared declare var testvar;.

test.js

var testvar = "Hello from external js";

index.html

...
  <link rel="icon" type="image/x-icon" href="assets/icon/favicon.ico">
  <link rel="manifest" href="manifest.json">
  <meta name="theme-color" content="#4e8ef7">

  <!-- cordova.js required for cordova apps -->
  <script src="cordova.js"></script>
  <script src="assets/js/test.js"></script> //here, not in body
...

app.componet.ts

declare var testvar;

@Component({
   templateUrl: 'app.html'
})
export class MyApp {
  @ViewChild(Nav) nav: Nav;
  constructor(private statusbar : StatusBar,  splashScreen: SplashScreen) {
   alert(testvar);
...

Remove it from index.html and use it like this:

import '../assets/data/test';

This is the solution that works for me on ionic 3.20.0:

1. Create this file src/assets/data/test.js. In this file declare these variables:

   testvar = "Hello from external js"; // notes: there is no var keywork testvar2 = "Hello from external js"; // notes: there is no var keywork var testvar3 = "Hello from external js"; // this will not work

2. In app.component.ts, add these lines to import the javascript file and declare its variables:

   import * as test from '../assets/data/test'; // check correct path declare var testvar: any; // each declaration should be on separate line declare var testvar2: any; declare var testvar3: any;

3. Now in app.component.ts, you can access those variables like this:

   console.log(testvar); // not test.testvar console.log(testvar2); console.log(testvar3); // will be undefined because of the var keywork

Final words: there is no need to add a link to test.js in src/index.html if we are doing like above.