如何在JavaScript中设置默认布尔值? [英] How to set default boolean values in JavaScript?

问题描述

在JavaScript中设置默认的可选值通常是通过||字符

Setting default optional values in JavaScript is usually done via the || character

var Car = function(color) {
  this.color = color || 'blue';
};

var myCar = new Car();
console.log(myCar.color); // 'blue'

var myOtherCar = new Car('yellow');
console.log(myOtherCar.color); // 'yellow'

之所以有效，是因为color是undefined，而undefined || String始终是String.当然，围绕String || undefined起作用的另一种方法是String.当出现两个Strings时，第一个获胜者'this' || 'that'是'this'.反之亦然，因为'that' || 'this'是'that'.

That works because color is undefined and undefined || String is always the String. Of course that also works the other way around String || undefined is String. When two Strings are present the first one wins 'this' || 'that' is 'this'. It does NOT work the other way around as 'that' || 'this' is 'that'.

问题是:如何使用布尔值实现相同的目标?

The question is: How can I achieve the same with boolean values?

以下面的示例为例

var Car = function(hasWheels) {
  this.hasWheels = hasWheels || true;
}

var myCar = new Car();
console.log(myCar.hasWheels); // true

var myOtherCar = new Car(false)
console.log(myOtherCar.hasWheels); // ALSO true !!!!!!

对于myCar，它起作用是因为undefined || true是true，但是如您所见，它对于myOtherCar不起作用，因为false || true是true.更改顺序无济于事，因为true || false仍然是true.

For myCar it works because undefined || true is true but as you can see it does NOT work for myOtherCar because false || true is true. Changing the order doesn't help as true || false is still true.

因此，我是否在这里遗漏了某些东西，或者以下是设置默认值的唯一方法吗?

Therefore, am I missing something here or is the following the only way to set the default value?

this.hasWheels = (hasWheels === false) ? false: true

干杯！

推荐答案

您可以执行以下操作:

this.hasWheels = hasWheels !== false;

这将为您提供一个true值，除非hasWheels是显式的false. (其他虚假的值，包括null和undefined，将导致true，我认为这是您想要的.)

That gets you a true value except when hasWheels is explicitly false. (Other falsy values, including null and undefined, will result in true, which I think is what you want.)

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