JavaScript-转换为Boolean类型

转换为 Boolean

var a = 123; //true
a = -123; //true
a = 0; //false
a = Infinity; //true
a = NaN; //false

//调用Boolean函数()来将a转换为布尔值
a = Boolean(a);

a = "";

a = Boolean(a);

a = null; //false
a = Boolean(a);

a = undefined; //false
a = Boolean(a);

console.log(typeof a);
console.log(a);

1. 使用 Boolean()函数

1.1. 数字 --> 布尔

• 除了 0 和 NaN,其余的都是 true

var a = 123; //true
a = -123; //true
a = 0; //false
a = Infinity; //true
a = NaN; //false

//调用Boolean函数()来将a转换为布尔值
a = Boolean(a);

console.log(typeof a);
console.log(a);

1.2. 字符串 --> 布尔

• 除了空串,其余的都是 true

var a = "";
a = Boolean(a);

console.log(typeof a);
console.log(a);

1.3. null 和 undefined 都会转换为 false

var a = null; //false
a = Boolean(a);

a = undefined; //false
a = Boolean(a);

console.log(typeof a);
console.log(a);

1.4. 对象也会转换为 true