How to dynamically inject a JavaScript function?

Question

I am stuck using a product with a horrible UI at work and trying to make it palatable via UserScripts in Chrome. To that end, I am trying to inject a JavaScript function into the page via the UserScripts mechanism:

// find the div
var dropDown = document.getElementById("tstGlobalNavigation_ddlChooseProject");

// inject function
dropDown.innerHTML = dropDown.innerHTML + "<script>function gotoIncident(){alert('111')}</script>";        

// inject a button
dropDown.innerHTML = dropDown.innerHTML + "&nbsp;&nbsp;&nbsp;<input type='button' name='btnSearch' value='Go' onClick='javascript:gotoIncident()' >";

As you can see I am injecting a button and a function (gotoIncident) that should fire when the user clicks the button.

The button does appear on the screen but when I click it, the javascript debugger tells me that gotoIncident is not defined.

What am I missing?

Community · Accepted Answer · 2020-06-20 09:12:55Z

10

Inject a <script> tag into the <head> which contains a self-invoking function:

var head = document.getElementsByTagName('head')[0],
    script = document.createElement('script');
    
script.src = 'path/to/script.js';    
head.appendChild(script);

Where the referenced script looks something like this:

(function(){
    // do your stuff here    
})();

Edit

How to do it as an inline script:

function fn() {
    alert('hello JS');
}

var head = ...,
    script = ...;
    
// FF doesn't support innerText
script[script.innerText ? 'innerText' : 'textContent'] = '(' + fn + ')()';
head.appendChild(script);

Demo

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Apr 6, 2011 at 23:46

Matt Ball

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2 Comments

AngryHacker Over a year ago

How do I do it inline? script.src='url' won't work, I need to define the function inline.

Karpak Over a year ago

This works perfectly fine if we make the last buy one line as shown below script[script.innerText ? 'innerText' : 'textContent'] = 'const fn=' + fn + '; fn();'; This also makes the function to be available through console

Michael Aaron Safyan · Accepted Answer · 2011-04-06 23:43:43Z

0

You need to define the function in the global scope (put it in the <head> section) to use it where you do.

answered Apr 6, 2011 at 23:43

Michael Aaron Safyan

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Comments

AngryHacker · Accepted Answer · 2011-05-12 18:40:50Z

For reference I resolved it the following way:

myDiv.innerHTML = myDiv.innerHTML + " <input type='text' id='txtSearch' name='txtSearch' style='position:absolute;top:8px;left:800px;width:50px' >";
myDiv.innerHTML = myDiv.innerHTML + " <input type='button' name='btnSearch' value='Go' onclick='fn()' style='position:absolute;top:8px;left:860px;width:35px'>";

addScript("function fn() {var obj = document.getElementById('txtSearch'); "
  + "if (obj != null) { "
  + "  var incidentId = document.getElementById('txtSearch').value; "
  + "  var currentURL = location.href; "
  + "  var splitResult = currentURL.split('/'); "
  + "  var projectId = splitResult[4]; "
  + "  location.href = 'http://site/SpiraTeam/' + projectId + '/Incident/' + incidentId + '.aspx'; "
  + " } }"
  , "fn");

}

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