js数据类型判断

判断数据类型，

1. typeof，能判断基本数据类型和函数，不能判断数组，数组要用其他方式判断

console.log(typeof 'abc') //string
console.log(typeof 1) //number
console.log(typeof {}) //object
console.log(typeof function(){}) //function
console.log(typeof Symbol()) //symbol
console.log(typeof []) //object typeof无法判断数组
console.log([] instanceof Array) //true 判断是否是数组

2. 借用Object的toString方法

console.log(Object.prototype.toString.call('a','string')) //[object String]
console.log(Object.prototype.toString.call(type)) //[object Function]
console.log(Object.prototype.toString.call(1)) //[object Number]
console.log(Object.prototype.toString.call({})) //[object Object]
console.log(Object.prototype.toString.call(true)) //[object Boolean]s
console.log(Object.prototype.toString.call([])) //[object Array]
console.log(Object.prototype.toString.call(Symbol())) //[object Symbol]

/**
 * 判断数据类型
 * @param {*} val  传入的数据
 * @param {*} type  传入某个类型'function','number','object','boolean','array','symbol','String' ，返回布尔值
 * @returns 
 */
function type(val,type) {
    var typeStr = Object.prototype.toString.call(val);
    typeStr = typeStr.slice(8,-1).toLowerCase()
    if(!type) return typeStr
    var types = ['function','number','object','boolean','array','symbol','string'];
    for(var i=0;i<types.length;i++){
        if(types[i] === type.toLowerCase()){
            return true
        }
    }
    return false
}
console.log(type('a')) //function
console.log(type(type)) //function
console.log(type(1)) //number
console.log(type({},'object')) //object
console.log(type(true,'string')) //false
console.log(type([],'array')) //true
console.log(type(Symbol(),'symbol')) //true