Getting the selected values in a multiselect tag in Javascript

Another approach for those who like a more functional style:

selections = Array.from(selectBox.options).filter(o => o.selected).map(o => o.value)

or

selections = Array.from(selectBox.selectedOptions).map(o => o.value)

Wouldn't this do it:

function searchFlights() {
    var select1 = document.getElementById("airports-select-1");
    var selected1 = [];
    for (var i = 0; i < select1.length; i++) {
        if (select1.options[i].selected) selected1.push(select1.options[i].value);
    }
    console.log(selected1);
}​

function searchFlights() {
    var select1 = document.getElementById("airports-select-1");
    var selected1 = [];
    for (var i = 0; i < select1.length; i++) {
        if (select1.options[i].selected) selected1.push(select1.options[i].value);
    }
    console.log(selected1);
}

<form method="post">
  <select name="Select1" multiple="multiple" size="8" id="airports-select-1" onblur="searchFlights()" ;>
    <option>aaa</option>
    <option>bbb</option>
    <option>ccc</option>
    <option>ddd</option>
    <option>eee</option>
  </select>
</form>

jsFiddle example

Update for 2018:

• If the <select> element contains a selectedOptions property, use that collection. The only browser still in wide circulation that doesn't support this is IE (any version). Edge does support it.

• If this is not supported, the answer by @j08691 is still correct, but as a performance optimization you can start iterating options at selectedIndex instead of 0. This is the index of the first selected option, or -1 if nothing is selected.