Question

If I manually enter text into an input element, I can call $("#myinput").val() and get a value.

If I set it first like $("#myinput").val("foo") and then call $("#myinput").val(), it returns nothing.

Answer 1

Make sure you have only one input on the page with id="myinput"

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Answer Based on Original Question:

$("input").val() returns the value of the first input of the page

if #myinput is not first, it will not be shown.

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To get all the vals of all the inputs on the page you can do:

$('input').each(function(){
    alert($(this).val());
});