Convert string in dot notation to get the object r

问题:

This question already has an answer here:

• Convert JavaScript string in dot notation into an object reference 24 answers

Consider this object in javascript,

var obj = { a : { b: 1, c: 2 } };

given the string \"obj.a.b\" how can I get the object this refers to, so that I may alter its value? i.e. I want to be able to do something like

obj.a.b = 5;
obj.a.c = 10;

where \"obj.a.b\" & \"obj.a.c\" are strings (not obj references). I came across this post where I can get the value the dot notation string is referring to obj but what I need is a way I can get at the object itself?

The nesting of the object may be even deeper than this. i.e. maybe

var obj = { a: { b: 1, c : { d : 3, e : 4}, f: 5 } }

回答1:

To obtain the value, consider:

function ref(obj, str) {
    str = str.split(\".\");
    for (var i = 0; i < str.length; i++)
        obj = obj[str[i]];
    return obj;
}

var obj = { a: { b: 1, c : { d : 3, e : 4}, f: 5 } }
str = \'a.c.d\'
ref(obj, str) // 3

or in a more fancy way, using reduce:

function ref(obj, str) {
    return str.split(\".\").reduce(function(o, x) { return o[x] }, obj);
}

Returning an assignable reference to an object member is not possible in javascript, you\'ll have to use a function like the following:

function set(obj, str, val) {
    str = str.split(\".\");
    while (str.length > 1)
        obj = obj[str.shift()];
    return obj[str.shift()] = val;
}

var obj = { a: { b: 1, c : { d : 3, e : 4}, f: 5 } }
str = \'a.c.d\'
set(obj, str, 99)
console.log(obj.a.c.d) // 99

or use ref given above to obtain the reference to the containing object and then apply the [] operator to it:

parts = str.split(/\\.(?=[^.]+$)/)  // Split \"foo.bar.baz\" into [\"foo.bar\", \"baz\"]
ref(obj, parts[0])[parts[1]] = 99

回答2:

Similar to thg435\'s answer, but with argument checks and supports nest levels where one of the ancestor levels isn\'t yet defined or isn\'t an object.

setObjByString = function(obj, str, val) {
    var keys, key;
    //make sure str is a string with length
    if (!str || !str.length || Object.prototype.toString.call(str) !== \"[object String]\") {
        return false;
    }
    if (obj !== Object(obj)) {
        //if it\'s not an object, make it one
        obj = {};
    }
    keys = str.split(\".\");
    while (keys.length > 1) {
        key = keys.shift();
        if (obj !== Object(obj)) {
            //if it\'s not an object, make it one
            obj = {};
        }
        if (!(key in obj)) {
            //if obj doesn\'t contain the key, add it and set it to an empty object
            obj[key] = {};
        }
        obj = obj[key];
    }
    return obj[keys[0]] = val;
};

Usage:

var obj;
setObjByString(obj, \"a.b.c.d.e.f\", \"hello\");

回答3:

If this javascript runs in a browser then you can access the object like this:

window[\'obj\'][\'a\'][\'b\'] = 5

So given the string \"obj.a.b\" you have to split the it by .:

var s = \"obj.a.b\"
var e = s.split(\".\")
window[e[0]][e[1]][e[2]] = 5

回答4:

Below is a simple class wrapper around dict:

class Dots(dict):
    def __init__(self, *args, **kargs):
            super(Dots, self).__init__(*args, **kargs)

    def __getitem__(self, key):
            try:
                    item = super(Dots, self).__getitem__(key)
            except KeyError:
                    item = Dots()
                    self.__setitem__(key, item)

            return Dots(item) if type(item) == dict else item

    def __setitem__(self, key, value):
            if type(value) == dict: value = Dots(value)
            super(Dots, self).__setitem__(key, value)

    __getattr__ = __getitem__
    __setattr__ = __setitem__

Example:

>>> a = Dots()
>>> a.b.c = 123
>>> a.b.c
123
>>> a.b
{\'c\': 123}
>>> a
{\'b\': {\'c\': 123}}

Missing key are created on the fly as empty Dots():

>>> if a.Missing: print \"Exists\"
...
>>> a
{\'Missing\': {}, \'b\': {\'c\': 123}}

回答5:

var obj = { a : { b: 1, c: 2 } };
walkObject(obj,\"a.b\"); // 1

function walkObject( obj, path ){
  var parts = path.split(\".\"), i=0, part;
  while (obj && (part=parts[i++])) obj=obj[part];
  return obj;
}

Or if you like your code terse:

function walkObject( o, path ){
  for (var a,p=path.split(\'.\'),i=0; o&&(a=p[i++]); o=o[a]);
  return o;
}

回答6:

Returning an assignable reference to an object member is not possible in javascript. You can assign value to a deep object member by dot notation with a single line of code like this.

new Function(\'_\', \'val\', \'_.\' + path + \' = val\')(obj, value);

In you case:

var obj = { a : { b: 1, c: 2 } };

new Function(\'_\', \'val\', \'_.a.b\' + \' = val\')(obj, 5); // Now obj.a.b will be equal to 5