What is the correct way to write this javascript function?

Question

I'm trying to understand javascript and javascript functions. This function is used to change the look of a button.

function changeButton(){
 btn.style.backgroundColor = btn.style.backgroundColor == "black" ? "white" : "black";
 btn.style.color = btn.style.color == "white" ? "black" : "white";
 btn.innerHTML = btn.innerHTML == 'GOOD JOB' ? 'CLICK ME' : 'GOOD JOB';
}

It works just fine. But when I look at this function I see a lot of repetition. The basic structure seems to be element = element == value1 ? value2 : value1

So in my mind this should work:

function toggleValue(elem, val1, val2){
 elem = elem == val1 ? val2 : val1
}
function changeButton(){
 var x = btn.style.backgroundColor
 var y = btn.style.color
 var z = btn.innerHTML
 toggleValue(x, 'white', 'black')
 toggleValue(y, 'black', 'white')
 toggleValue(z, 'CLICK ME', 'GOOD JOB')
}

But it does not work and I don't understand why. Can someone tell me why this doesn't work? And is there a way to make it work?

• georg: A better way would be to use CSS and classList.toggle to turn the "active" class on and off.
• deceze: x.y = ... modifies the property of an object. x = ... reassigns a local variable.
• Bharadwaj: var x = btn.style.backgroundColor, in this you are just copying a value which is there in the backgroundColor property. This will not act as a reference.

Answer 1

It does not work, because you hand over a primitive value an not a reference to the property.

function toggleValue(elem, prop, val1, val2){
 elem[prop] = elem[prop] == val1 ? val2 : val1
}
function changeButton(){
 toggleValue(btn.style, 'backgroundColor', 'white', 'black')
 toggleValue(btn.style, 'color', 'black', 'white')
 toggleValue(btn, 'innerHTML', 'CLICK ME', 'GOOD JOB')
}

Answer 2

Because you are passing the String which is immutable.

You can create one more argument - property.

function toggleValue(elem, prop, val1, val2){
 elem[prop] = elem[prop] == val1 ? val2 : val1
}
function changeButton(){
 var x = btn.style;
 var y = btn.style;
 var z = btn;
 toggleValue(x, "backgroundColor", 'white', 'black');
 toggleValue(y, "color", 'black', 'white');
 toggleValue(z, "innerHTML", 'CLICK ME', 'GOOD JOB');
}

Answer 3

function toggleValue(elem, val1, val2, ButtonStyleType) { 
 elem = elem == val1 ? val2 : val1;
 if (ButtonStyleType == 'backgroundColor')
 btn.style.backgroundColor = elem;
 else if (ButtonStyleType == 'color')
 btn.style.color = elem;
 else if (ButtonStyleType == 'innerHtml')
 btn.innerHTML = elem;
 }
 function changeButton() { 
 var x = btn.style.backgroundColor;
 var y = btn.style.color;
 var z = btn.innerHTML;
 toggleValue(x, 'green', 'yellow', 'backgroundColor');
 toggleValue(y, 'black', 'Orange', 'color');
 toggleValue(z, 'Default', 'GOOD JOB', 'innerHtml');
 }

<button id="btn" style="background-color:green; color:black;">Default</button><br />
 <br />
 <a style="cursor:pointer;color:blue;" onclick="changeButton();">Click here to update button style</a>

Answer 4

You have to understand the difference between pass by value and pass by reference to know more about that click here