How To Pass Input(type = Text ) From A Html Form To Javascript Function

i want to pass the udid taken from textfield to function getusername. Enter Udid :

Solution 2:

Try this code:

In your html:

<inputtype="button" value="Get User Name(udid)" onclick="getUserName(document.getElementById('udid'));">

Function javascript:

function getUserName(id){
    alert(id.value);
}

Look at this demo: JSFIDDLE