直接双叹号即可 !!值
当有值时:非空字符串
,空数组
、空对象
;输出为 true
;
当没值时:""
、null
、undefined
;输出为false
示例js代码
let obj1 = ''
console.log('"":',!!obj1)
let obj2 = null
console.log('null:',!!obj2)
let obj3 = undefined
console.log('undefined:',!!obj3)
let obj4 = []
console.log('有值[]:',!!obj4)
let obj5 = {
}
console.log('有值{}:',!!obj5)
let obj6 = '哈哈'
console.log('有值"哈哈":',!!obj6)