我想这样做：
if(a.b.c) alert('c exists') //produces error
if(a && a.b && a.b.c ) alert('c exists') //also produces ReferenceError
if(typeof(a) != "undefined" && a.b && a.b.c) alert('c exists');
或某种类似的功能……
if(exists('a.b.c')) alert('c exists');
function exists(varname){
vars=varname.split('.');
for(i=0;i<vars.length;i++){
//iterate through each object and check typeof
}
}
//this wont work with local variables inside a function
编辑：解决方案以下
(相信Felix的这个主题,我只是稍微调整了一下
Check if object member exists in nested object)
这有效：
if (typeof a != 'undefined' && a.b && a.b.c) alert('c exists')
但我找到的最好的事情就是把它放到一个函数中.我使用了2个不同的函数,一个用于在对象中获取变量,另一个用于检查其是否设置.
/**
* Safely retrieve a property deep in an object of objects/arrays
* such as userObj.contact.email
* @usage var email=getprop(userObj,'contact.email')
* This would retrieve userObj.contact.email,or return FALSE without
* throwing an error,if userObj or contact obj did not exist
* @param obj OBJECT - the base object from which to retrieve the property out of
* @param path_string STRING - a string of dot notation of the property relative to
* @return MIXED - value of obj.eval(path_string),OR FALSE
*/
function getprop(obj,path_string)
{
if(!path_string) return obj
var arr = path_string.split('.'),val = obj || window;
for (var i = 0; i < arr.length; i++) {
val = val[arr[i]];
if ( typeof val == 'undefined' ) return false;
if ( i==arr.length-1 ) {
if (val=="") return false
return val
}
}
return false;
}
/**
* Check if a proprety on an object exists
* @return BOOL
*/
function isset(obj,path_string)
{
return (( getprop(obj,path_string) === false ) ? false : true)
}
解决方法
这个怎么样：
function exists(str,namespace) {
var arr = str.split('.'),val = namespace || window;
for (var i = 0; i < arr.length; i++) {
val = val[arr[i]];
if ( typeof val == 'undefined' ) return false;
}
return true;
}
