Boolean() 构造函数

¥Syntax

new Boolean(value)
Boolean(value)

注意：Boolean() 可以与 new 一起调用，也可以不与 new 一起调用，但效果不同。参见 返回值。

¥Note: Boolean() can be called with or without new, but with different effects. See Return value.

¥Parameters

value

Boolean 对象的初始值。

¥Return value

当 Boolean() 作为构造函数（与 new）被调用时，它会创建一个 Boolean 对象，该对象不是基元。

¥When Boolean() is called as a constructor (with new), it creates a Boolean object, which is not a primitive.

当 Boolean() 作为函数调用时（没有 new），它将参数强制为布尔原语。

¥When Boolean() is called as a function (without new), it coerces the parameter to a boolean primitive.

警告：你应该很少发现自己使用 Boolean 作为构造函数。

¥Warning: You should rarely find yourself using Boolean as a constructor.

¥Description

作为第一个参数传递的值为 转换为布尔值。如果该值被省略或者是 0、-0、0n、null、false、NaN、undefined 或空字符串 ("")，则该对象的初始值为 false。所有其他值，包括任何对象、空数组 ([]) 或字符串 "false"，都会创建一个初始值为 true 的对象。

¥The value passed as the first parameter is converted to a boolean value. If the value is omitted or is 0, -0, 0n, null, false, NaN, undefined, or the empty string (""), then the object has an initial value of false. All other values, including any object, an empty array ([]), or the string "false", create an object with an initial value of true.

注意：当非标准属性 document.all 用作此构造函数的参数时，结果是值为 false 的 Boolean 对象。此属性是遗留的且非标准的，不应使用。

¥Note: When the non-standard property document.all is used as an argument for this constructor, the result is a Boolean object with the value false. This property is legacy and non-standard and should not be used.

¥Examples

¥Creating Boolean objects with an initial value of false

const bZero = new Boolean(0);
const bNull = new Boolean(null);
const bEmptyString = new Boolean("");
const bfalse = new Boolean(false);

typeof bfalse; // "object"
Boolean(bfalse); // true

请注意，使用 Boolean() 将 Boolean 对象转换为基元总是会产生 true，即使该对象拥有 false 的值。因此，始终建议你避免构造 Boolean 封装对象。

¥Note how converting a Boolean object to a primitive with Boolean() always yields true, even if the object holds a value of false. You are therefore always advised to avoid constructing Boolean wrapper objects.

如果需要从封装对象中取出原始值，请使用该对象的 valueOf() 方法，而不是使用 Boolean() 函数。

¥If you need to take the primitive value out from the wrapper object, instead of using the Boolean() function, use the object's valueOf() method instead.

const bfalse = new Boolean(false);

bfalse.valueOf(); // false

¥Creating Boolean objects with an initial value of true

const btrue = new Boolean(true);
const btrueString = new Boolean("true");
const bfalseString = new Boolean("false");
const bSuLin = new Boolean("Su Lin");
const bArrayProto = new Boolean([]);
const bObjProto = new Boolean({});

¥See also

• 布尔值