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。
今天刚刚编写了这个函数,它对嵌套对象中的属性进行了深入搜索,如果找到了,则返回该属性的值。
/**
* Performs a deep search looking for the existence of a property in a
* nested object. Supports namespaced search: Passing a string with
* a parent sub-object where the property key may exist speeds up
* search, for instance: Say you have a nested object and you know for
* certain the property/literal you're looking for is within a certain
* sub-object, you can speed the search up by passing "level2Obj.targetProp"
* @param {object} obj Object to search
* @param {object} key Key to search for
* @return {*} Returns the value (if any) located at the key
*/
var getPropByKey = function( obj, key ) {
var ret = false, ns = key.split("."),
args = arguments,
alen = args.length;
// Search starting with provided namespace
if ( ns.length > 1 ) {
obj = (libName).getPropByKey( obj, ns[0] );
key = ns[1];
}
// Look for a property in the object
if ( key in obj ) {
return obj[key];
} else {
for ( var o in obj ) {
if ( (libName).isPlainObject( obj[o] ) ) {
ret = (libName).getPropByKey( obj[o], key );
if ( ret === 0 || ret === undefined || ret ) {
return ret;
}
}
}
}
return false;
}
基于这个答案,我使用ES2015提出了一个通用函数,可以解决这个问题
function validChain( object, ...keys ) {
return keys.reduce( ( a, b ) => ( a || { } )[ b ], object ) !== undefined;
}
var test = {
first: {
second: {
third: "This is not the key your are looking for"
}
}
}
if ( validChain( test, "first", "second", "third" ) ) {
console.log( test.first.second.third );
}
一个简短的ES5版本@CMS的优秀答案:
// Check the obj has the keys in the order mentioned. Used for checking JSON results.
var checkObjHasKeys = function(obj, keys) {
var success = true;
keys.forEach( function(key) {
if ( ! obj.hasOwnProperty(key)) {
success = false;
}
obj = obj[key];
})
return success;
}
通过类似测试:
var test = { level1:{level2:{level3:'result'}}};
utils.checkObjHasKeys(test, ['level1', 'level2', 'level3']); // true
utils.checkObjHasKeys(test, ['level1', 'level2', 'foo']); // false
我尝试了递归方法:
function objHasKeys(obj, keys) {
var next = keys.shift();
return obj[next] && (! keys.length || objHasKeys(obj[next], keys));
}
这个keys.length||退出递归,这样它就不会在没有键可供测试的情况下运行函数。测验:
obj = {
path: {
to: {
the: {
goodKey: "hello"
}
}
}
}
console.log(objHasKeys(obj, ['path', 'to', 'the', 'goodKey'])); // true
console.log(objHasKeys(obj, ['path', 'to', 'the', 'badKey'])); // undefined
我正在使用它打印一组具有未知键/值的对象的友好html视图,例如:
var biosName = objHasKeys(myObj, 'MachineInfo:BiosInfo:Name'.split(':'))
? myObj.MachineInfo.BiosInfo.Name
: 'unknown';