2018-10-10 22:03:03 +00:00
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---
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id: 587d7dbe367417b2b2512bb8
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2021-03-07 16:15:14 +00:00
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title: 使用 @if 和 @else 为样式添加逻辑
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2018-10-10 22:03:03 +00:00
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challengeType: 0
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2020-09-07 08:11:08 +00:00
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forumTopicId: 301463
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2021-01-13 02:31:00 +00:00
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dashedName: use-if-and-else-to-add-logic-to-your-styles
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2021-03-07 16:15:14 +00:00
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Sass 中的 `@if` 指令对于测试特定情况非常有用——它的工作方式与 JavaScript 中的 `if` 语句类似。
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2020-09-07 08:11:08 +00:00
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```scss
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@mixin make-bold($bool) {
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@if $bool == true {
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font-weight: bold;
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}
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}
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```
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2021-03-07 16:15:14 +00:00
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类似 JavaScript,可以在 Sass 中使用 `@else if` 和 `@else` 测试更多条件:
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2020-09-07 08:11:08 +00:00
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```scss
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@mixin text-effect($val) {
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@if $val == danger {
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color: red;
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}
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@else if $val == alert {
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color: yellow;
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}
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@else if $val == success {
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color: green;
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}
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@else {
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color: black;
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}
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}
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```
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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创建一个名为 `border-stroke` 的 mixin,它接受一个参数 `$val`。 mixin 应使用 `@if`,`@else if` 和 `@else` 检查以下条件:
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2020-09-07 08:11:08 +00:00
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```scss
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light - 1px solid black
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medium - 3px solid black
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heavy - 6px solid black
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```
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2021-03-07 16:15:14 +00:00
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如果 `$val` 不是 `light`、`medium` 或者 `heavy`,border 应该设置为 `none`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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应该声明一个名为 `border-stroke` 的 mixin,它有一个名为 `$val` 的参数。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(code.match(/@mixin\s+?border-stroke\s*?\(\s*?\$val\s*?\)\s*?{/gi));
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2018-10-10 22:03:03 +00:00
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```
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2021-03-07 16:15:14 +00:00
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mixin 应该有一个 `@if` 语句来检查 `$val` 是否等于 `light`,并将 `border` 设置为 `1px solid black`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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code.match(
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/@if\s+?\$val\s*?===?\s*?light\s*?{\s*?border\s*?:\s*?1px\s+?solid\s+?black\s*?;\s*?}/gi
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)
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);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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mixin 应该有一个 `@else if` 语句来检查 `$val` 是否等于 `medium`,并设置 `border` 为 `3px solid black`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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code.match(
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/@else\s+?if\s+?\$val\s*?===?\s*?medium\s*?{\s*?border\s*?:\s*?3px\s+?solid\s+?black\s*?;\s*?}/gi
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)
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);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-07 16:15:14 +00:00
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mixin 应该有一个 `@else if` 语句来检查 `$val` 是否等于 `heavy`,并设置 `border` 为 `3px solid black`。
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2020-09-07 08:11:08 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(
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code.match(
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/@else\s+?if\s+?\$val\s*?===?\s*?heavy\s*?{\s*?border\s*?:\s*?6px\s+?solid\s+?black\s*?;\s*?}/gi
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)
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);
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```
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2020-09-07 08:11:08 +00:00
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2021-03-07 16:15:14 +00:00
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mixin 应该有一个 `@else` 语句来将 `border` 设置为 `none`。
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2020-09-07 08:11:08 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(code.match(/@else\s*?{\s*?border\s*?:\s*?none\s*?;\s*?}/gi));
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2018-10-10 22:03:03 +00:00
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```
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2020-08-13 15:24:35 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --seed-contents--
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```html
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<style type='text/scss'>
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#box {
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width: 150px;
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height: 150px;
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background-color: red;
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@include border-stroke(medium);
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}
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</style>
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<div id="box"></div>
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```html
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<style type='text/scss'>
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@mixin border-stroke($val) {
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@if $val == light {
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border: 1px solid black;
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}
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@else if $val == medium {
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border: 3px solid black;
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}
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@else if $val == heavy {
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border: 6px solid black;
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}
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@else {
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border: none;
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}
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}
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#box {
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width: 150px;
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height: 150px;
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background-color: red;
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@include border-stroke(medium);
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}
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</style>
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<div id="box"></div>
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```
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