布尔运算符

与 JavaScript 等语言不同，Sass 使用单词而不是符号作为 布尔值 运算符。

  • not <expression> 返回表达式值的相反值：它将 true 变成 false，将 false 变成 true。

    ¥not <expression> returns the opposite of the expression’s value: it turns true into false and false into true.

  • 如果两个表达式的值都是 true，则 <expression> and <expression> 返回 true；如果其中一个表达式的值为 false，则返回 false。

    ¥<expression> and <expression> returns true if both expressions’ values are true, and false if either is false.

  • 如果任一表达式的值为 true，则 <expression> or <expression> 返回 true；如果两者均为 false，则返回 false。

    ¥<expression> or <expression> returns true if either expression’s value is true, and false if both are false.

Playground

SCSS Syntax

@debug not true; // false
@debug not false; // true

@debug true and true; // true
@debug true and false; // false

@debug true or false; // true
@debug false or false; // false
Playground

Sass Syntax

@debug not true  // false
@debug not false  // true

@debug true and true  // true
@debug true and false  // false

@debug true or false  // true
@debug false or false  // false

Truthiness and FalsinessTruthiness and Falsiness permalink

Anywhere true or false are allowed, you can use other values as well. The values false and null are falsey, which means Sass considers them to indicate falsehood and cause conditions to fail. Every other value is considered truthy, so Sass considers them to work like true and cause conditions to succeed.

For example, if you want to check if a string contains a space, you can just write string.index($string, " "). The string.index() function returns null if the string isn’t found and a number otherwise.

⚠️ Heads up!

Some languages consider more values falsey than just false and null. Sass isn’t one of those languages! Empty strings, empty lists, and the number 0 are all truthy in Sass.