js判断类型

        <input type="file" id="file">
        <script type="text/javascript">        
        //首字母大写
	let firstUpperCase = ([first, ...rest]) => first.toUpperCase() + rest.join('')
        //判断obj是不是classname类型
	let isSomeClass = (obj,className)=>Object.prototype.toString.call(obj)===`[object ${firstUpperCase(className)}]`;
	window.onload=function(){
        //使用方法
	    var file = document.getElementById("file");
	    file.onchange=info=>{
		    console.log(isSomeClass(file.files[0],'File'));//true
	    }
	    let arr = [1,2,3];
	    console.log(isSomeClass(arr,'Array'))//判断其他类型:true
	    console.log(isSomeClass(arr,'array'))//首字母自动大写:true
	    console.log(isSomeClass(arr,'string'))//首字母自动大写:false
    }
	</script>