检查对象是否为空的最快方法是什么?
有没有比这更快更好的方法:
function count_obj(obj){
var i = 0;
for(var key in obj){
++i;
}
return i;
}
当前回答
我修改了肖恩·维埃拉的代码来满足我的需要。Null和undefined根本不算作对象，数字、布尔值和空字符串返回false。
'use strict'; // Speed up calls to hasOwnProperty var hasOwnProperty = Object.prototype.hasOwnProperty; var isObjectEmpty = function(obj) { // null and undefined are not empty if (obj == null) return false; if(obj === false) return false; if(obj === true) return false; if(obj === "") return false; if(typeof obj === "number") { return false; } // Assume if it has a length property with a non-zero value // that that property is correct. if (obj.length > 0) return false; if (obj.length === 0) return true; // Otherwise, does it have any properties of its own? // Note that this doesn't handle // toString and valueOf enumeration bugs in IE < 9 for (var key in obj) { if (hasOwnProperty.call(obj, key)) return false; } return true; }; exports.isObjectEmpty = isObjectEmpty;
其他回答
https://lodash.com/docs#isEmpty非常方便:
_.isEmpty({}) // true
_.isEmpty() // true
_.isEmpty(null) // true
_.isEmpty("") // true
对于ECMAScript5(不是所有浏览器都支持)，你可以使用:
Object.keys(obj).length === 0
假设你有以下对象:
var obj1= {};
var obj2= {test: "test"};
不要忘记我们不能使用===符号来测试对象是否相等，因为他们得到继承，所以如果你使用ECMA 5和更高版本的javascript，答案很简单，你可以使用下面的函数:
function isEmpty(obj) {
//check if it's an Obj first
var isObj = obj !== null
&& typeof obj === 'object'
&& Object.prototype.toString.call(obj) === '[object Object]';
if (isObj) {
for (var o in obj) {
if (obj.hasOwnProperty(o)) {
return false;
break;
}
}
return true;
} else {
console.error("isEmpty function only accept an Object");
}
}
结果如下:
isEmpty(obj1); //this returns true
isEmpty(obj2); //this returns false
isEmpty([]); // log in console: isEmpty function only accept an Object
不需要图书馆。
function(){ //must be within a function
var obj = {}; //the object to test
for(var isNotEmpty in obj) //will loop through once if there is a property of some sort, then
return alert('not empty')//what ever you are trying to do once
return alert('empty'); //nope obj was empty do this instead;
}
情况有多糟?
function(obj){
for(var key in obj){
return false; // not empty
}
return true; // empty
}
