如果我有对象的引用:
var test = {};
可能(但不是立即)具有嵌套对象,例如:
{level1: {level2: {level3: "level3"}}};
检查深度嵌套对象中是否存在属性的最佳方法是什么?
警报(测试级别1);生成未定义,但警告(test.level1.level2.level3);失败。
我目前正在做这样的事情:
if(test.level1 && test.level1.level2 && test.level1.level2.level3) {
alert(test.level1.level2.level3);
}
但我想知道是否有更好的方法。
这个功能怎么样?它不需要单独列出每个嵌套属性,而是保持“dot”语法(尽管是字符串),使其更具可读性。如果未找到属性,则返回undefined或指定的默认值,如果找到,则返回属性的值。
val(obj, element, default_value)
// Recursively checks whether a property of an object exists. Supports multiple-level nested properties separated with '.' characters.
// obj = the object to test
// element = (string or array) the name of the element to test for. To test for a multi-level nested property, separate properties with '.' characters or pass as array)
// default_value = optional default value to return if the item is not found. Returns undefined if no default_value is specified.
// Returns the element if it exists, or undefined or optional default_value if not found.
// Examples: val(obj1, 'prop1.subprop1.subsubprop2');
// val(obj2, 'p.r.o.p', 'default_value');
{
// If no element is being requested, return obj. (ends recursion - exists)
if (!element || element.length == 0) { return obj; }
// if the element isn't an object, then it can't have properties. (ends recursion - does not exist)
if (typeof obj != 'object') { return default_value; }
// Convert element to array.
if (typeof element == 'string') { element = element.split('.') }; // Split on dot (.)
// Recurse into the list of nested properties:
let first = element.shift();
return val(obj[first], element, default_value);
}
我的解决方案,我使用了很长时间(使用字符串不幸,找不到更好的)
function get_if_exist(str){
try{return eval(str)}
catch(e){return undefined}
}
// way to use
if(get_if_exist('test.level1.level2.level3')) {
alert(test.level1.level2.level3);
}
// or simply
alert(get_if_exist('test.level1.level2.level3'));
edit:只有当对象“test”具有全局范围/范围时,这才有效。否则您必须执行以下操作:
// i think it's the most beautiful code I have ever write :p
function get_if_exist(obj){
return arguments.length==1 || (obj[arguments[1]] && get_if_exist.apply(this,[obj[arguments[1]]].concat([].slice.call(arguments,2))));
}
alert(get_if_exist(test,'level1','level2','level3'));
编辑最终版本以允许2种调用方法:
function get_if_exist(obj){
var a=arguments, b=a.callee; // replace a.callee by the function name you choose because callee is depreceate, in this case : get_if_exist
// version 1 calling the version 2
if(a[1] && ~a[1].indexOf('.'))
return b.apply(this,[obj].concat(a[1].split('.')));
// version 2
return a.length==1 ? a[0] : (obj[a[1]] && b.apply(this,[obj[a[1]]].concat([].slice.call(a,2))));
}
// method 1
get_if_exist(test,'level1.level2.level3');
// method 2
get_if_exist(test,'level1','level2','level3');
下面是我的看法-这些解决方案中的大多数都忽略了嵌套数组的情况,如:
obj = {
"l1":"something",
"l2":[{k:0},{k:1}],
"l3":{
"subL":"hello"
}
}
我可能想检查obj.l2[0].k
使用下面的函数,您可以执行深度测试('l2[0].k',obj)
如果对象存在,函数将返回true,否则返回false
函数deeptest(keyPath,testObj){变量obj;keyPath=keyPath.split('.')var cKey=keyPath.shift();函数get(pObj,pKey){var bracketStart,bracketEnd,o;bracketStart=pKey.indexOf(“[”);if(bracketStart>-1){//检查嵌套数组bracketEnd=pKey.indexOf(“]”);var arrIndex=pKey.substr(bracketStart+1,bracketEnd-bracketStart-1);pKey=pKey.substr(0,括号开始);var n=pObj[pKey];o=n?n[arrIndex]:未定义;}其他{o=pObj[pKey];}返回o;}obj=获取(testObj,cKey);while(obj&&keyPath.length){obj=get(obj,keyPath.shift());}返回typeof(obj)!=='未定义';}变量obj={“l1”:“级别1”,“arr1”:[{“k”:0},{“k”:1},{“k”:2}],“子”:{“a”:“字母a”,“b”:“字母b”}};console.log(“l1:”+深度测试(“l1”,obj));console.log(“arr1[0]:”+深度测试(“arr1[0]”,obj));console.log(“arr1[1].k:”+深度测试(“arr1].k”,obj));console.log(“arr1[1].j:”+深度测试(“arr1].j”,obj));console.log(“arr1[3]:”+深度测试(“arr1[3]”,obj));console.log(“arr2:”+深度测试(“arr2”,obj));
根据@Stephane LaFlèche的回答,我提出了另一个剧本版本。
JSFiddle演示
var obj = {"a":{"b":{"c":"Hello World"}},"resTest":"potato","success":"This path exists"};
checkForPathInObject = function(object,path,value) {
var pathParts = path.split("."),
result = false;
// Check if required parameters are set; if not, return false
if(!object || typeof object == 'undefined' || !path || typeof path != 'string')
return false;
/* Loop through object keys to find a way to the path or check for value
* If the property does not exist, set result to false
* If the property is an object, update @object
* Otherwise, update result */
for(var i=0;i<pathParts.length;i++){
var currentPathPart = pathParts[i];
if(!object.hasOwnProperty( currentPathPart )) {
result = false;
} else if (object[ currentPathPart ] && path == pathParts[i]) {
result = pathParts[i];
break;
} else if(typeof object[ currentPathPart ] == 'object') {
object = object[ currentPathPart ];
} else {
result = object[ currentPathPart ];
}
}
/* */
if(typeof value != 'undefined' && value == result)
return true;
return result;
};
// Uncomment the lines below to test the script
// alert( checkForPathInObject(obj,'a.b.c') ); // Results "Hello World"
// alert( checkForPathInObject(obj,'a.success') ); // Returns false
// alert( checkForPathInObject(obj,'resTest', 'potato') ); // Returns true