How can I disable an option in a select box based on its value in JavaScript?

// Get all options within <select id='foo'>...</select>
var op = document.getElementById("foo").getElementsByTagName("option");
for (var i = 0; i < op.length; i++) {
  // lowercase comparison for case-insensitivity
  (op[i].value.toLowerCase() == "stackoverflow") 
    ? op[i].disabled = true 
    : op[i].disabled = false ;
}

Without enabling non-targeted elements:

// Get all options within <select id='foo'>...</select>
var op = document.getElementById("foo").getElementsByTagName("option");
for (var i = 0; i < op.length; i++) {
  // lowercase comparison for case-insensitivity
  if (op[i].value.toLowerCase() == "stackoverflow") {
    op[i].disabled = true;
  }
}

jQuery

With jQuery you can do this with a single line:

$("option[value='optionvalue']")
  .attr("disabled", "disabled")
  .siblings().removeAttr("disabled");

Without enabling non-targeted elements:

$("option[value='optionvalue']").attr("disabled", "disabled");

Note that this is not case insensitive. “optionvalue” will not equal “optionvalue”. To get a case-insensitive match, you’d have to cycle through each, converting the value to a lower case, and then check against that:

$("option").each(function(){
  if ($(this).val().toLowerCase() == "stackoverflow") {
    $(this).attr("disabled", "disabled").siblings().removeAttr("disabled");
  }
});

Without enabling non-targeted elements:

$("option").each(function(){
  if ($(this).val().toLowerCase() == "stackoverflow") {
    $(this).attr("disabled", "disabled");
  }
});