How do I add another javascript code that works seperate from the first one? [duplicate]

This question already has an answer here:

• Add two functions to window.onload 12 answers

<script>



function fillText() {
        var myswitch = document.getElementById("myonoffswitch");
        var mytextarea= document.getElementById("mytextarea");
        myswitch.onchange = function(){
            if(this.checked){
                mytextarea.value = "Hi there" 
            }else{
                mytextarea.value = "Bye bye"
            }
        }
    }
    window.onload = fillText;



</script>

<input type="checkbox" id="myonoffswitch">Switch</input>


 <textarea name="text" id="mytextarea" style="width:100%;resize: none;" cols="25" rows="10">
Some text 1

</textarea>

The code above shows a textarea with a switch checkbox (javascript). If you click the checkbox it will change the text in the textarea. The code above works fine. But the problem is when I try to add another one, so another switch and another textbox...

I just tried to copy paste the code with a different id name etc. but somehow it disables the first box:

<script>



function fillText() {
        var myswitch = document.getElementById("myonoffswitch");
        var mytextarea= document.getElementById("mytextarea");
        myswitch.onchange = function(){
            if(this.checked){
                mytextarea.value = "Hi there" 
            }else{
                mytextarea.value = "Bye bye"
            }
        }
    }
    window.onload = fillText;



</script>

<script>



function fillText() {
        var myswitch2 = document.getElementById("myonoffswitch2");
        var mytextarea2= document.getElementById("mytextarea2");
        myswitch.onchange = function(){
            if(this.checked){
                mytextarea2.value = "Hi there" 
            }else{
                mytextarea2.value = "Bye bye"
            }
        }
    }
    window.onload = fillText;



</script>

<input type="checkbox" id="myonoffswitch">Switch</input>


 <textarea name="text" id="mytextarea" style="width:100%;resize: none;" cols="25" rows="10">
Some text 1

</textarea>

<input type="checkbox" id="myonoffswitch2">Switch</input>


 <textarea name="text" id="mytextarea2" style="width:100%;resize: none;" cols="25" rows="10">

Some text 2

</textarea>