小程序或js，判断变量（Undefined String Array Object）是否为空

function isBlank(str){
if (Object.prototype.toString.call(str) ==='[object Undefined]'){//空
return true
} else if (
Object.prototype.toString.call(str) === '[object String]' ||
Object.prototype.toString.call(str) === '[object Array]') { //字条串或数组
return str.length==0?true:false
} else if (Object.prototype.toString.call(str) === '[object Object]') {
return JSON.stringify(str)=='{}'?true:false
}else{
return true
}

}

const formatTime = date => {
const year = date.getFullYear()
const month = date.getMonth() + 1
const day = date.getDate()
const hour = date.getHours()
const minute = date.getMinutes()
const second = date.getSeconds()

return [year, month, day].map(formatNumber).join('/') + ' ' + [hour, minute, second].map(formatNumber).join(':')
}

/**
* 用于判断空，Undefined String Array Object
*/
function isBlank(str){
if (Object.prototype.toString.call(str) ==='[object Undefined]'){//空
return true
} else if (
Object.prototype.toString.call(str) === '[object String]' ||
Object.prototype.toString.call(str) === '[object Array]') { //字条串或数组
return str.length==0?true:false
} else if (Object.prototype.toString.call(str) === '[object Object]') {
return JSON.stringify(str)=='{}'?true:false
}else{
return true
}

}

/**
* 导出
*/
module.exports = {
formatTime: formatTime,
String:{
isBlank: isBlank
}
}

import { String } from '../../utils/util.js';
var xx = '';
if( String.isBlank(xx))
//xx is blank