如何在JavaScript中选择操作之前设置默认变量值

Question

I am completely new to JavaScript, so far i have been able to learn how to get values from my select drop down. However one other thing I would like to do is have a default value which gets displayed when a user visits the page. Then change with the select action. Currently I get no value displayed until after selecting from the drop down. I have tried to search but i have not found any easy to understand guide on how to implement this. See my code below

 function val() { d = document.getElementById("select_year").value; document.getElementById("demo").innerHTML = d; } 

 <select onchange="val()" id="select_year"> <option selected value="2017">2017</option> <option value="2016">2016</option> <option value="2015">2015</option> </select> <p id="demo"></p> 

Answer 1

Seems like you have just to call your function.

 function val() { d = document.getElementById("select_year").value; document.getElementById("demo").innerHTML = d; } val(); 

 <select onchange="val()" id="select_year"> <option selected value="2017">2017</option> <option value="2016">2016</option> <option value="2015">2015</option> </select> <p id="demo"></p> 

Answer 2

Just make a small change.

<option selected="selected" value="122"></option>

this will be good.