Answers for "if checkbox is checked javascript"

javacript is checkbox checked

//using plane javascript 
if(document.getElementById('on_or_off_checkbox').checked) {
    //I am checked
} 

//using jQuery
if($('#on_or_off_checkbox').is(':checked')){
    //I am checked
}

if checkbox is checked

if ($('#id_input').is(':checked')) { }

oncheck checkbox javascript

<input type='checkbox' onchange='handleChange(this);'> Checkbox

function handleChange(checkbox) {
    if(checkbox.checked == true){
        document.getElementById("submit").removeAttribute("disabled");
    }else{
        document.getElementById("submit").setAttribute("disabled", "disabled");
   }
}