jQuery: Test if checkbox is NOT checked

One reliable way I use is:

if($("#checkSurfaceEnvironment-1").prop('checked') == true){    //do something}

If you want to iterate over checked elements use the parent element

$("#parentId").find("checkbox").each(function(){    if ($(this).prop('checked')==true){         //do something    }});

More info:

This works well because all checkboxes have a property checked which stores the actual state of the checkbox. If you wish you can inspect the page and try to check and uncheck a checkbox, and you will notice the attribute "checked" (if present) will remain the same. This attribute only represents the initial state of the checkbox, and not the current state. The current state is stored in the property checked of the dom element for that checkbox.

See Properties and Attributes in HTML

if (!$("#checkSurfaceEnvironment-1").is(":checked")) {    // do something if the checkbox is NOT checked}

You can also use either jQuery .not() method or :not() selector:

if ($('#checkSurfaceEnvironment').not(':checked').length) {    // do stuff for not selected}

JSFiddle Example

Additional Notes

From the jQuery API documentation for the :not() selector:

The .not() method will end up providing you with more readable selections than pushing complex selectors or variables into a :not()selector filter. In most cases, it is a better choice.