Javascript doesn't work on Chrome Extension

Question

My HTML has 2 buttons and a text input. They change the value of the input (-1 and +1).

It just works fine on the code snippet here, but doesn't work on Chrome Extension.

My HTML file calls the JavaScript file, and it is on the manifest too:

 <script type="text/javascript" src="melionline.js"></script> 

Manifest:

 { "manifest_version":2, "name": "Online Console", "version":"1.0", "description": "Simulador de consola de Online", "browser_action":{ "default_icon": "icon24.png", "default_popup": "PrincipalOnline.html" }, "permissions":[ "activeTab" ], "content_scripts": [ { "js": [ "melionline.js" ]}] } 

 document.getElementById("plus").addEventListener("click", changeValue) var cant=1; function changeValue() { if (cant < 5) { cant += 0.5; } else { cant = 5; } var valor = document.getElementById("counter"); valor.value = cant.toString(); } document.getElementById("minus").addEventListener("click", changeValue2) function changeValue2() { if (cant >1) { cant -= 1; } else { cant = 1; } var valor = document.getElementById("counter"); valor.value = cant.toString(); } 

 <button id="minus" style="width:6px; text-align:center;" type="button" class="btn btn-default">-</button> <input style="text-align:center; width:30px; height:30px;" type="text" id="counter" value="1"> <button style="text-align:center; width:6px;" type="button" id="plus" class="btn btn-default" onclick= "changeValue()" >+</button>