返回操作数之一的布尔运算符 [英] Boolean operators which return one of the operands

问题描述

在Python以及Javascript中，布尔值or和and运算符将返回其中一个操作数，而不是true或false.

In Python, and maybe in Javascript, the boolean or and and operators return one of the operands, instead of true or false.

• 在Python中，返回操作数之一:'' || 'hello' == 'hello'
• 相比之下，在PHP中:'' || 'hello' == true;

• In Python, one of the operands is returned: '' || 'hello' == 'hello'
• In comparison, in PHP: '' || 'hello' == true;

现在

• 如何调用布尔运算符的这种行为?
• 在所有浏览器中都可以使用Javascript吗?

推荐答案

为空合并运算符，&&是空安全合并运算符( 要链接的链接，如果可以找到一个链接，抱歉，我找不到链接.

As Ignacio's answer points out, these are coalescing operators. || is the null coalescing operator, && is the null-safe coalescing operator (link to follow, if I can find one sorry, I can't find a link).

它们应该在所有浏览器中可用-它们都在ECMA-262第1，第2，第3和第5版中进行了定义，大多数当前的Javascript实现均基于第3或第5版.从ECMA-262第3版开始:

They should be available in all browsers - they are both defined in the ECMA-262 1st, 2nd, 3rd and 5th editions, most current Javascript implementations are based upon 3rd or 5th. From ECMA-262 3rd edition:

生产LogicalANDExpression:LogicalANDExpression&&按位计算ORExpression为 如下:
1.评估LogicalANDExpression.
2.调用GetValue(Result(1)).
3.调用ToBoolean(Result(2)).
4.如果Result(3)为false，则返回Result(2).
5.评估BitwiseORExpression.
6.调用GetValue(Result(5)).
7.返回结果(6).

The production LogicalANDExpression : LogicalANDExpression && BitwiseORExpression is evaluated as follows:
1. Evaluate LogicalANDExpression.
2. Call GetValue(Result(1)).
3. Call ToBoolean(Result(2)).
4. If Result(3) is false, return Result(2).
5. Evaluate BitwiseORExpression.
6. Call GetValue(Result(5)).
7. Return Result(6).

生产LogicalORExpression:LogicalORExpression || LogicalANDExpression计算为 如下:
1.评估LogicalORExpression.
2.调用GetValue(Result(1)).
3.调用ToBoolean(Result(2)).
4.如果Result(3)为true，则返回Result(2).
5.评估LogicalANDExpression.
6.调用GetValue(Result(5)).
7.返回结果(6).

The production LogicalORExpression : LogicalORExpression || LogicalANDExpression is evaluated as follows:
1. Evaluate LogicalORExpression.
2. Call GetValue(Result(1)).
3. Call ToBoolean(Result(2)).
4. If Result(3) is true, return Result(2).
5. Evaluate LogicalANDExpression.
6. Call GetValue(Result(5)).
7. Return Result(6).

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