Halp

HTML

<form>
  <input type="checkbox" id="someId">
  <label for="someid">Some label</label>
  <button type="submit">Submit</button>
</form>
<form>
  <input type="checkbox" id="someOtherId">
  <label for="someOtherId">Other label</label>
  <input type="submit" value="Submit">
</form>
<form>
  <input type="checkbox" id="andAnotherId">
  <label for="andAnotherId">Another label</label>
  <button type="submit">Submit</button>
</form>

JavaScript

var allForms = document.querySelectorAll('form');

for ( var i = 0, len = allForms.length; i < len; i++ ) {
	allForms[i].style.color = "red"; //test
  
	var agreementCheckbox = allForms[i].querySelectorAll('form input[type="checkbox"]');
  var submitButton = allForms[i].querySelectorAll('form *[type="submit"]');
  submitButton[0].disabled = true;
  
  //agreementCheckbox[0].onchange = getCheckboxValue; //Works
  //agreementCheckbox[0].onchange = getCheckboxValue(submitButton[0]); //Does not work :(
  agreementCheckbox[0].onchange = handler(' world');
}

function handler(a){
  return function (e){
    alert('hello' + a);
  }
}
function getCheckboxValue (submitButton) {
  if ( this.checked ) {
  	alert ('Чекбокс включен');
  } else {
    alert ('Чекбокс выключен');
  }
}