Jquery select all values in a multiselect dropdown

I have a multi-select html dropdown. I want to programatically (via jquery) select开发者_运维技巧 all values in the dropdown. How can I do this?

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Where the select has the id test

$('#test option').attr('selected', 'selected');

JSFiddle Example

Or as Ryan mentioned you can use .prop

$('#test option').prop('selected', true); // or pass false to deselect them

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Simply do $("#dropdown").val([0, 1, 2, 3]) where 0, 1, 2, 3 the values you want to select.