title: How to Include JS file in ionic 3
body: <p>Im looking for a way to access a variable from external js file which i included in assets/data folder</p>
  
  <p>below is what i tried</p>
  
  <p>placed <strong><code>test.js</code></strong> in <strong>assets/data folder</strong></p>
  
  <p>in <strong><code>test.js</code></strong> added variable <code>testvar = "heloo from external js";</code></p>
  
  <p>added script tag in <code>src/index.html</code> <code>&lt;script src="assets/data/test.js"&gt;&lt;/script&gt;</code></p>
  
  <p>in <code>app.component.ts</code> i added this line after imports;<code>declare var testvar: any;</code></p>
  
  <p>in constructor added this line to log the value <code>console.log(testvar);</code></p>
  
  <p>result is <strong><em>error</em></strong> : <strong><em>ERROR ReferenceError: testvar is not defined</em></strong></p>
  
  <p>so, how can i use my js variable in typescript ?</p>