LESS CSS guards without mixin

Question

I'm just getting into LESS and am trying to figure out how I can make conditional css statements without mixins. I find that I have a lot of single line css statements that only occur once but are dependent on some variable or condition and that using mixins is a bit pointless since it will never be reused.

Example.

@add-margin: true;

body {
    margin-top: 20px;  //I only want this if add-margin is true
}

So ideally I want this:

body when (@add-margin) {
     margin-top: 20px;
}

But that doesn't work. Using a mixin works but seems silly to make one just for a one liner. Is there some alternative way I can do this?

Thanks

Answer 1

yes you can, it's similar to your code.

@add-margin: true;

.margin() when (@add-margin) {
    margin-top: 20px;
}

body { .margin(); }

UPDATE: Using the latest versions of LESS (1.5+), usage of "guarded mixins" are not required to achieve this, and you could use "css gaurds" instead, therefore the OP's code will work out of the box

Answer 2

CSS Guards feature was introduced in Less v1.5.0 and hence now we can use guards the same way as mentioned in the question.

@add-margin: true;

body when (@add-margin){
    margin-top: 20px;
}

If in case, you need to assign multiple such properties to different selectors based on the same variable, it can be implemented like below using the & selector.

& when (@add-margin){
    body{
        margin-top: 20px;
    }
    h1{
        margin-top: 10px;
    }
}

Note: As mentioned by memeLab in comments, any value for the @add-margin variable other than true are considered as falsy. This is because true is a keyword whereas 'true' is a String value. For example, the below would output nothing.

@add-margin: 'true';

body when (@add-margin){
    margin-top: 20px;
}

However, the below would work because it does a String comparison.

@add-margin: 'true';

body when (@add-margin = 'true'){
    margin-top: 20px;
}

If you are using Less compiler lower than v1.5.0 then the answer posted by Unicornist is the best bet.

Answer 3

no, it is not possible in that form.

you could use a variable equal to 0 or 1 and multiply by 20 and then always output a rule, or use JavaScript (i would advise you to avoid this) to convert true to 0 or 20 and always output a rule, but if you want the property added conditionally, you need guards.