globally-defined-variables.md

Globally defined variables

When using .inject() to put a script into the current page, it seems reasonable that it would behave like any <script> tag, like the following:

<script src='http://somecdn.tld/files/your-injected-file.js'></script>

...or:

<script>
  //your script injected here
</script>

.inject() does not add a script tag. Instead, the injected javascript is run through a template that puts the script inside of a function scope. Any implicit globally defined variable will not be available on the global scope. Consider the following Nightmare script:

var Nightmare = require('nightmare'),
    path = require('path'),
    nightmare = Nightmare();

nightmare.goto('http://example.com')
    .inject('js', path.resolve(__dirname, 'inject.js'))
    .evaluate(function(){
        return globalVariable;
    })
    .end()
    .then(function(globalVariable){
        console.log('global variable: ' + globalVariable);
    });

The inject.js script injected above:

var globalVariable = 'hello world!';

The above is executing a case similar to the following:

var response = function(){
  globalVariable = 'hello world!';
}
return globalVariable;

Since globalVariable has fallen out of scope, it can no longer be accessed. Nightmare will hang as globalVariable being undefined causes a runtime exception. Implicit global variables are common to older versions of jQuery that expose $ as a global variable instead of attaching to window.

Solution

Patch global variables explicitly onto window. If the injected script from above was altered like so:

window.globalVariable = 'hello world!';

... the Nightmare script behaves as expected.

References

• .inject() Documentation
• Nightmare #524