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| --- | |
| layout: "post" | |
| title: "Variables" | |
| date: 2014-06-12 | |
| description: "Setting and using variables, scoping variables, default variable values, property lookup" | |
| --- | |
| CSS is extremely repetitive. And if you are working on a big, complex project you will have identical values/colors all around the place. When the time comes for a minor modification or a global refactoring chances are that you will forget to change something somewhere. | |
| This article is covers only basic uses of variables, for more advanced use check the [Variable Interpolation article](/variable-interpolation). | |
| Here is the basic syntax for variables. | |
| <%- @code('Variables', 'basic') %> | |
| ## Lazy loaded variables | |
| Only Less supports lazy-loaded variables - you can type the variable even after the place you are calling it from and it will work. For example, this Less code works: | |
| <%- @code('Variables', 'lazy') %> | |
| ## Default values | |
| Default values for variables work just like regular values, but if both are declared, the latter will take precedence. | |
| Such default values can be useful for cases when you are not sure whether a regular value for a variable is or will be declared. | |
| <%- @code('Variables', 'default') %> | |
| Less does not support setting a default variable, this has been [discussed before](https://github.com/less/less.js/pull/313) [a](https://github.com/less/less.js/pull/1104) [number](https://github.com/less/less.js/issues/1109) [of](https://github.com/less/less.js/pull/1705) [times](https://github.com/less/less.js/issues/1706) and Less is unlikely to get this feature, as its variables are lazy-loaded (see the previous section) and this may lead to confusion. | |
| ## Scoped variables | |
| All preprocessors support scoped variables - they work only within the context they are defined in, and can be useful to avoid interference with similarly named variables. | |
| Scoped variables work only within the current selector and all child selectors. | |
| Note that Stylus allows another way of doing this - by defining the variable and the value at the same time. | |
| <%- @code('Variables', 'scoped') %> | |
| ## Property lookup | |
| Stylus supports another feature that is not yet present in other preprocessors - property lookup. | |
| It works close to how scoped variables operate. In the example below you will see that the `.child` bubbles up until it finds a `@foo`. | |
| <%- @code('Variables', 'lookup') %> | |
| Property lookups, just like scoped variables are a great way to center an object. For example, you can set a negative `margin-left` that is half the width of the object, and a `margin-top` that is half its height, in addition to `left: 50%` and `right: 50%`. | |
| ## Variables accept many formats | |
| All preprocessors allow you to set the following data types as variables | |
| * numbers, with or without units - `1.25`, `16`, `10px`, `1.1em`, `320deg` | |
| * strings of text, with and without quotes - `"foo"`, `'bar'`, `baz` | |
| * colors - `red`, `#41ea07`, `hsl(333, 56, 43)`, `rgba(255, 0, 0, 0.5)` | |
| * boolean values - `true`, `false` | |
| * nulls - `null` | |
| * lists of values, separated by spaces or commas - `1.5em 1em 0 2em`, `Helvetica, Arial, sans-serif` | |
| In addition to the above, Sass and Stylus support mapping values from maps/hashes, something that Less is currently lacking. | |