问题
I have a data structure like this :
var someObject = {
'part1' : {
'name': 'Part 1',
'size': '20',
'qty' : '50'
},
'part2' : {
'name': 'Part 2',
'size': '15',
'qty' : '60'
},
'part3' : [
{
'name': 'Part 3A',
'size': '10',
'qty' : '20'
}, {
'name': 'Part 3B',
'size': '5',
'qty' : '20'
}, {
'name': 'Part 3C',
'size': '7.5',
'qty' : '20'
}
]
};
And I would like to access the data using these variable :
var part1name = "part1.name";
var part2quantity = "part2.qty";
var part3name1 = "part3[0].name";
part1name should be filled with someObject.part1.name 's value, which is "Part 1". Same thing with part2quantity which filled with 60.
Is there anyway to achieve this with either pure javascript or JQuery?
回答1:
I just made this based on some similar code I already had, it appears to work:
Object.byString = function(o, s) {
s = s.replace(/\[(\w+)\]/g, '.$1'); // convert indexes to properties
s = s.replace(/^\./, ''); // strip a leading dot
var a = s.split('.');
for (var i = 0, n = a.length; i < n; ++i) {
var k = a[i];
if (k in o) {
o = o[k];
} else {
return;
}
}
return o;
}
Usage::
Object.byString(someObj, 'part3[0].name');
See a working demo at http://jsfiddle.net/alnitak/hEsys/
EDIT some have noticed that this code will throw an error if passed a string where the left-most indexes don't correspond to a correctly nested entry within the object. This is a valid concern, but IMHO best addressed with a try / catch block when calling, rather than having this function silently return undefined for an invalid index.
回答2:
This is the solution I use:
function resolve(path, obj=self, separator='.') {
var properties = Array.isArray(path) ? path : path.split(separator)
return properties.reduce((prev, curr) => prev && prev[curr], obj)
}
Example usage:
// accessing property path on global scope
resolve("document.body.style.width")
// or
resolve("style.width", document.body)
// accessing array indexes
// (someObject has been defined in the question)
resolve("part3.0.size", someObject) // returns '10'
// accessing non-existent properties
// returns undefined when intermediate properties are not defined:
resolve('properties.that.do.not.exist', {hello:'world'})
// accessing properties with unusual keys by changing the separator
var obj = { object: { 'a.property.name.with.periods': 42 } }
resolve('object->a.property.name.with.periods', obj, '->') // returns 42
// accessing properties with unusual keys by passing a property name array
resolve(['object', 'a.property.name.with.periods'], obj) // returns 42
Limitations:
- Can't use brackets (
[]) for array indices—though specifying array indices between the separator token (e.g.,.) works fine as shown above.
回答3:
This is now supported by lodash using _.get(obj, property). See https://lodash.com/docs#get
Example from the docs:
var object = { 'a': [{ 'b': { 'c': 3 } }] };
_.get(object, 'a[0].b.c');
// → 3
_.get(object, ['a', '0', 'b', 'c']);
// → 3
_.get(object, 'a.b.c', 'default');
// → 'default'
回答4:
You'd have to parse the string yourself:
function getProperty(obj, prop) {
var parts = prop.split('.');
if (Array.isArray(parts)) {
var last = parts.pop(),
l = parts.length,
i = 1,
current = parts[0];
while((obj = obj[current]) && i < l) {
current = parts[i];
i++;
}
if(obj) {
return obj[last];
}
} else {
throw 'parts is not valid array';
}
}
This required that you also define array indexes with dot notation:
var part3name1 = "part3.0.name";
It makes the parsing easier.
DEMO
回答5:
ES6: Only one line in Vanila JS (it return null if don't find instead of giving error):
'path.string'.split('.').reduce((p,c)=>p&&p[c]||null, MyOBJ)
Or example:
'a.b.c'.split('.').reduce((p,c)=>p&&p[c]||null, {a:{b:{c:1}}})
For a ready to use function that also recognizes false, 0 and negative number and accept default values as parameter:
const resolvePath = (object, path, defaultValue) => path
.split('.')
.reduce((o, p) => o ? o[p] : defaultValue, object)
Example to use:
resolvePath(window,'document.body') => <body>
resolvePath(window,'document.body.xyz') => undefined
resolvePath(window,'document.body.xyz', null) => null
resolvePath(window,'document.body.xyz', 1) => 1
Bonus:
To set a path (Requested by @rob-gordon) you can use:
const setPath = (object, path, value) => path
.split('.')
.reduce((o,p,i) => o[p] = path.split('.').length === ++i ? value : o[p] || {}, object)
Example:
let myVar = {}
setPath(myVar, 'a.b.c', 42) => 42
console.log(myVar) => {a: {b: {c: 42}}}
Access array with []:
const resolvePath = (object, path, defaultValue) => path
.split(/[\.\[\]\'\"]/)
.filter(p => p)
.reduce((o, p) => o ? o[p] : defaultValue, object)
Example:
const myVar = {a:{b:[{c:1}]}}
resolvePath(myVar,'a.b[0].c') => 1
resolvePath(myVar,'a["b"][\'0\'].c') => 1
回答6:
Works for arrays / arrays inside the object also. Defensive against invalid values.
/**
* Retrieve nested item from object/array
* @param {Object|Array} obj
* @param {String} path dot separated
* @param {*} def default value ( if result undefined )
* @returns {*}
*/
function path(obj, path, def){
var i, len;
for(i = 0,path = path.split('.'), len = path.length; i < len; i++){
if(!obj || typeof obj !== 'object') return def;
obj = obj[path[i]];
}
if(obj === undefined) return def;
return obj;
}
//////////////////////////
// TEST //
//////////////////////////
var arr = [true, {'sp ace': true}, true]
var obj = {
'sp ace': true,
arr: arr,
nested: {'dotted.str.ing': true},
arr3: arr
}
shouldThrow(`path(obj, "arr.0")`);
shouldBeDefined(`path(obj, "arr[0]")`);
shouldBeEqualToNumber(`path(obj, "arr.length")`, 3);
shouldBeTrue(`path(obj, "sp ace")`);
shouldBeEqualToString(`path(obj, "none.existed.prop", "fallback")`, "fallback");
shouldBeTrue(`path(obj, "nested['dotted.str.ing'])`);<script src="https://cdn.rawgit.com/coderek/e7b30bac7634a50ad8fd/raw/174b6634c8f57aa8aac0716c5b7b2a7098e03584/js-test.js"></script>回答7:
using eval:
var part1name = eval("someObject.part1.name");
wrap to return undefined on error
function path(obj, path) {
try {
return eval("obj." + path);
} catch(e) {
return undefined;
}
}
http://jsfiddle.net/shanimal/b3xTw/
Please use common sense and caution when wielding the power of eval. It's a bit like a light saber, if you turn it on there's a 90% chance you'll sever a limb. Its not for everybody.
回答8:
You can manage to obtain value of a deep object member with dot notation without any external JavaScript library with the simple following trick:
new Function('_', 'return _.' + path)(obj);
In your case to obtain value of part1.name from someObject just do:
new Function('_', 'return _.part1.name')(someObject);
Here is a simple fiddle demo: https://jsfiddle.net/harishanchu/oq5esowf/
回答9:
This will probably never see the light of day... but here it is anyway.
- Replace
[]bracket syntax with. - Split on
.character - Remove blank strings
- Find the path (otherwise
undefined)
// "one liner" (ES6)
const deep_value = (obj, path) =>
path
.replace(/\[|\]\.?/g, '.')
.split('.')
.filter(s => s)
.reduce((acc, val) => acc && acc[val], obj);
// ... and that's it.
var someObject = {
'part1' : {
'name': 'Part 1',
'size': '20',
'qty' : '50'
},
'part2' : {
'name': 'Part 2',
'size': '15',
'qty' : '60'
},
'part3' : [
{
'name': 'Part 3A',
'size': '10',
'qty' : '20'
}
// ...
]
};
console.log(deep_value(someObject, "part1.name")); // Part 1
console.log(deep_value(someObject, "part2.qty")); // 60
console.log(deep_value(someObject, "part3[0].name")); // Part 3A回答10:
It's a one liner with lodash.
const deep = { l1: { l2: { l3: "Hello" } } };
const prop = "l1.l2.l3";
const val = _.reduce(prop.split('.'), function(result, value) { return result ? result[value] : undefined; }, deep);
// val === "Hello"
Or even better...
const val = _.get(deep, prop);
Or ES6 version w/ reduce...
const val = prop.split('.').reduce((r, val) => { return r ? r[val] : undefined; }, deep);
Plunkr
回答11:
I think you are asking for this:
var part1name = someObject.part1.name;
var part2quantity = someObject.part2.qty;
var part3name1 = someObject.part3[0].name;
You could be asking for this:
var part1name = someObject["part1"]["name"];
var part2quantity = someObject["part2"]["qty"];
var part3name1 = someObject["part3"][0]["name"];
Both of which will work
Or maybe you are asking for this
var partName = "part1";
var nameStr = "name";
var part1name = someObject[partName][nameStr];
Finally you could be asking for this
var partName = "part1.name";
var partBits = partName.split(".");
var part1name = someObject[partBits[0]][partBits[1]];
回答12:
Here I offer more ways, which seem faster in many respects:
Option 1: Split string on . or [ or ] or ' or ", reverse it, skip empty items.
function getValue(path, origin) {
if (origin === void 0 || origin === null) origin = self ? self : this;
if (typeof path !== 'string') path = '' + path;
var parts = path.split(/\[|\]|\.|'|"/g).reverse(), name; // (why reverse? because it's usually faster to pop off the end of an array)
while (parts.length) { name=parts.pop(); if (name) origin=origin[name]; }
return origin;
}
Option 2 (fastest of all, except eval): Low level character scan (no regex/split/etc, just a quick char scan).
Note: This one does not support quotes for indexes.
function getValue(path, origin) {
if (origin === void 0 || origin === null) origin = self ? self : this;
if (typeof path !== 'string') path = '' + path;
var c = '', pc, i = 0, n = path.length, name = '';
if (n) while (i<=n) ((c = path[i++]) == '.' || c == '[' || c == ']' || c == void 0) ? (name?(origin = origin[name], name = ''):(pc=='.'||pc=='['||pc==']'&&c==']'?i=n+2:void 0),pc=c) : name += c;
if (i==n+2) throw "Invalid path: "+path;
return origin;
} // (around 1,000,000+/- ops/sec)
Option 3: (new: option 2 expanded to support quotes - a bit slower, but still fast)
function getValue(path, origin) {
if (origin === void 0 || origin === null) origin = self ? self : this;
if (typeof path !== 'string') path = '' + path;
var c, pc, i = 0, n = path.length, name = '', q;
while (i<=n)
((c = path[i++]) == '.' || c == '[' || c == ']' || c == "'" || c == '"' || c == void 0) ? (c==q&&path[i]==']'?q='':q?name+=c:name?(origin?origin=origin[name]:i=n+2,name='') : (pc=='['&&(c=='"'||c=="'")?q=c:pc=='.'||pc=='['||pc==']'&&c==']'||pc=='"'||pc=="'"?i=n+2:void 0), pc=c) : name += c;
if (i==n+2 || name) throw "Invalid path: "+path;
return origin;
}
JSPerf: http://jsperf.com/ways-to-dereference-a-delimited-property-string/3
"eval(...)" is still king though (performance wise that is). If you have property paths directly under your control, there shouldn't be any issues with using 'eval' (especially if speed is desired). If pulling property paths "over the wire" (on the line!? lol :P), then yes, use something else to be safe. Only an idiot would say to never use "eval" at all, as there ARE good reasons when to use it. Also, "It is used in Doug Crockford's JSON parser." If the input is safe, then no problems at all. Use the right tool for the right job, that's it.
回答13:
Speigg's approach is very neat and clean, though I found this reply while searching for the solution of accessing AngularJS $scope properties by string path and with a little modification it does the job:
$scope.resolve = function( path, obj ) {
return path.split('.').reduce( function( prev, curr ) {
return prev[curr];
}, obj || this );
}
Just place this function in your root controller and use it any child scope like this:
$scope.resolve( 'path.to.any.object.in.scope')
回答14:
Just in case, anyone's visiting this question in 2017 or later and looking for an easy-to-remember way, here's an elaborate blog post on Accessing Nested Objects in JavaScript without being bamboozled by
Cannot read property 'foo' of undefined error
Access Nested Objects Using Array Reduce
Let's take this example structure
const user = {
id: 101,
email: 'jack@dev.com',
personalInfo: {
name: 'Jack',
address: [{
line1: 'westwish st',
line2: 'washmasher',
city: 'wallas',
state: 'WX'
}]
}
}
To be able to access nested arrays, you can write your own array reduce util.
const getNestedObject = (nestedObj, pathArr) => {
return pathArr.reduce((obj, key) =>
(obj && obj[key] !== 'undefined') ? obj[key] : undefined, nestedObj);
}
// pass in your object structure as array elements
const name = getNestedObject(user, ['personalInfo', 'name']);
// to access nested array, just pass in array index as an element the path array.
const city = getNestedObject(user, ['personalInfo', 'address', 0, 'city']);
// this will return the city from the first address item.
There is also an excellent type handling minimal library typy that does all this for you.
With typy, your code will look like this
const city = t(user, 'personalInfo.address[0].city').safeObject;
Disclaimer: I am the author of this package.
回答15:
I haven't yet found a package to do all of the operations with a string path, so I ended up writing my own quick little package which supports insert(), get() (with default return), set() and remove() operations.
You can use dot notation, brackets, number indices, string number properties, and keys with non-word characters. Simple usage below:
> var jsocrud = require('jsocrud');
...
// Get (Read) ---
> var obj = {
> foo: [
> {
> 'key w/ non-word chars': 'bar'
> }
> ]
> };
undefined
> jsocrud.get(obj, '.foo[0]["key w/ non-word chars"]');
'bar'
https://www.npmjs.com/package/jsocrud
https://github.com/vertical-knowledge/jsocrud
回答16:
Simple function, allowing for either a string or array path.
function get(obj, path) {
if(typeof path === 'string') path = path.split('.');
if(path.length === 0) return obj;
return get(obj[path[0]], path.slice(1));
}
const obj = {a: {b: {c: 'foo'}}};
console.log(get(obj, 'a.b.c')); //foo
OR
console.log(get(obj, ['a', 'b', 'c'])); //foo
回答17:
There is an npm module now for doing this: https://github.com/erictrinh/safe-access
Example usage:
var access = require('safe-access');
access(very, 'nested.property.and.array[0]');
回答18:
/**
* Access a deep value inside a object
* Works by passing a path like "foo.bar", also works with nested arrays like "foo[0][1].baz"
* @author Victor B. https://gist.github.com/victornpb/4c7882c1b9d36292308e
* Unit tests: http://jsfiddle.net/Victornpb/0u1qygrh/
*/
function getDeepVal(obj, path) {
if (typeof obj === "undefined" || obj === null) return;
path = path.split(/[\.\[\]\"\']{1,2}/);
for (var i = 0, l = path.length; i < l; i++) {
if (path[i] === "") continue;
obj = obj[path[i]];
if (typeof obj === "undefined" || obj === null) return;
}
return obj;
}
Works with
getDeepVal(obj,'foo.bar')
getDeepVal(obj,'foo.1.bar')
getDeepVal(obj,'foo[0].baz')
getDeepVal(obj,'foo[1][2]')
getDeepVal(obj,"foo['bar'].baz")
getDeepVal(obj,"foo['bar']['baz']")
getDeepVal(obj,"foo.bar.0.baz[1]['2']['w'].aaa[\"f\"].bb")
回答19:
While reduce is good, I am surprised no one used forEach:
function valueForKeyPath(obj, path){
const keys = path.split('.');
keys.forEach((key)=> obj = obj[key]);
return obj;
};
Test
回答20:
If you need to access different nested key without knowing it at coding time (it will be trivial to address them) you can use the array notation accessor:
var part1name = someObject['part1']['name'];
var part2quantity = someObject['part2']['qty'];
var part3name1 = someObject['part3'][0]['name'];
They are equivalent to the dot notation accessor and may vary at runtime, for example:
var part = 'part1';
var property = 'name';
var part1name = someObject[part][property];
is equivalent to
var part1name = someObject['part1']['name'];
or
var part1name = someObject.part1.name;
I hope this address your question...
EDIT
I won't use a string to mantain a sort of xpath query to access an object value. As you have to call a function to parse the query and retrieve the value I would follow another path (not :
var part1name = function(){ return this.part1.name; }
var part2quantity = function() { return this['part2']['qty']; }
var part3name1 = function() { return this.part3[0]['name'];}
// usage: part1name.apply(someObject);
or, if you are uneasy with the apply method
var part1name = function(obj){ return obj.part1.name; }
var part2quantity = function(obj) { return obj['part2']['qty']; }
var part3name1 = function(obj) { return obj.part3[0]['name'];}
// usage: part1name(someObject);
The functions are shorter, clearer, the interpreter check them for you for syntax errors and so on.
By the way, I feel that a simple assignment made at right time will be sufficent...
回答21:
Just had the same question recently and successfully used https://npmjs.org/package/tea-properties which also set nested object/arrays :
get:
var o = {
prop: {
arr: [
{foo: 'bar'}
]
}
};
var properties = require('tea-properties');
var value = properties.get(o, 'prop.arr[0].foo');
assert(value, 'bar'); // true
set:
var o = {};
var properties = require('tea-properties');
properties.set(o, 'prop.arr[0].foo', 'bar');
assert(o.prop.arr[0].foo, 'bar'); // true
回答22:
Inspired by @webjay's answer: https://stackoverflow.com/a/46008856/4110122
I made this function which can you use it to Get/ Set/ Unset any value in object
function Object_Manager(obj, Path, value, Action)
{
try
{
if(Array.isArray(Path) == false)
{
Path = [Path];
}
let level = 0;
var Return_Value;
Path.reduce((a, b)=>{
level++;
if (level === Path.length)
{
if(Action === 'Set')
{
a[b] = value;
return value;
}
else if(Action === 'Get')
{
Return_Value = a[b];
}
else if(Action === 'Unset')
{
delete a[b];
}
}
else
{
return a[b];
}
}, obj);
return Return_Value;
}
catch(err)
{
console.error(err);
return obj;
}
}
To use it:
// Set
Object_Manager(Obj,[Level1,Level2,Level3],New_Value, 'Set');
// Get
Object_Manager(Obj,[Level1,Level2,Level3],'', 'Get');
// Unset
Object_Manager(Obj,[Level1,Level2,Level3],'', 'Unset');
回答23:
I'm developing online-shop with React. I tried to change values in copied state object to update original state with it on submit. Examples above haven't worked for me, because most of them mutate structure of copied object. I found working example of the function for accessing and changing values of the deep nested object properties: https://lowrey.me/create-an-object-by-path-in-javascript-2/ Here it is:
const createPath = (obj, path, value = null) => {
path = typeof path === 'string' ? path.split('.') : path;
let current = obj;
while (path.length > 1) {
const [head, ...tail] = path;
path = tail;
if (current[head] === undefined) {
current[head] = {};
}
current = current[head];
}
current[path[0]] = value;
return obj;
};
回答24:
The solutions here are just for accessing the deeply nested keys. I needed one for accessing, adding, modifying and deleting the keys. This is what I came up with:
var deepAccessObject = function(object, path_to_key, type_of_function, value){
switch(type_of_function){
//Add key/modify key
case 0:
if(path_to_key.length === 1){
if(value)
object[path_to_key[0]] = value;
return object[path_to_key[0]];
}else{
if(object[path_to_key[0]])
return deepAccessObject(object[path_to_key[0]], path_to_key.slice(1), type_of_function, value);
else
object[path_to_key[0]] = {};
}
break;
//delete key
case 1:
if(path_to_key.length === 1){
delete object[path_to_key[0]];
return true;
}else{
if(object[path_to_key[0]])
return deepAccessObject(object[path_to_key[0]], path_to_key.slice(1), type_of_function, value);
else
return false;
}
break;
default:
console.log("Wrong type of function");
}
};
path_to_key: path in an array. You can replace it by yourstring_path.split(".").type_of_function: 0 for accessing(dont pass any value tovalue), 0 for add and modify. 1 for delete.
回答25:
Building off of Alnitak's answer:
if(!Object.prototype.byString){
//NEW byString which can update values
Object.prototype.byString = function(s, v, o) {
var _o = o || this;
s = s.replace(/\[(\w+)\]/g, '.$1'); // CONVERT INDEXES TO PROPERTIES
s = s.replace(/^\./, ''); // STRIP A LEADING DOT
var a = s.split('.'); //ARRAY OF STRINGS SPLIT BY '.'
for (var i = 0; i < a.length; ++i) {//LOOP OVER ARRAY OF STRINGS
var k = a[i];
if (k in _o) {//LOOP THROUGH OBJECT KEYS
if(_o.hasOwnProperty(k)){//USE ONLY KEYS WE CREATED
if(v !== undefined){//IF WE HAVE A NEW VALUE PARAM
if(i === a.length -1){//IF IT'S THE LAST IN THE ARRAY
_o[k] = v;
}
}
_o = _o[k];//NO NEW VALUE SO JUST RETURN THE CURRENT VALUE
}
} else {
return;
}
}
return _o;
};
}
This allows you to set a value as well!
I've created an npm package and github with this as well
回答26:
Instead of a string an array can be used adressing nested objects and arrays e.g.: ["my_field", "another_field", 0, "last_field", 10]
Here is an example that would change a field based on this array representation. I am using something like that in react.js for controlled input fields that change the state of nested structures.
let state = {
test: "test_value",
nested: {
level1: "level1 value"
},
arr: [1, 2, 3],
nested_arr: {
arr: ["buh", "bah", "foo"]
}
}
function handleChange(value, fields) {
let update_field = state;
for(var i = 0; i < fields.length - 1; i++){
update_field = update_field[fields[i]];
}
update_field[fields[fields.length-1]] = value;
}
handleChange("update", ["test"]);
handleChange("update_nested", ["nested","level1"]);
handleChange(100, ["arr",0]);
handleChange('changed_foo', ["nested_arr", "arr", 3]);
console.log(state);
回答27:
Based on a previous answer, I have created a function that can also handle brackets. But no dots inside them due to the split.
function get(obj, str) {
return str.split(/\.|\[/g).map(function(crumb) {
return crumb.replace(/\]$/, '').trim().replace(/^(["'])((?:(?!\1)[^\\]|\\.)*?)\1$/, (match, quote, str) => str.replace(/\\(\\)?/g, "$1"));
}).reduce(function(obj, prop) {
return obj ? obj[prop] : undefined;
}, obj);
}
回答28:
// (IE9+) Two steps
var pathString = "[0]['property'].others[3].next['final']";
var obj = [{
property: {
others: [1, 2, 3, {
next: {
final: "SUCCESS"
}
}]
}
}];
// Turn string to path array
var pathArray = pathString
.replace(/\[["']?([\w]+)["']?\]/g,".$1")
.split(".")
.splice(1);
// Add object prototype method
Object.prototype.path = function (path) {
try {
return [this].concat(path).reduce(function (f, l) {
return f[l];
});
} catch (e) {
console.error(e);
}
};
// usage
console.log(obj.path(pathArray));
console.log(obj.path([0,"doesNotExist"]));回答29:
Working with Underscore's property or propertyOf:
var test = {
foo: {
bar: {
baz: 'hello'
}
}
}
var string = 'foo.bar.baz';
// document.write(_.propertyOf(test)(string.split('.')))
document.write(_.property(string.split('.'))(test));<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js"></script>Good Luck...
回答30:
Extension of Mohamad Hamouday' Answer will fill in missing keys
function Object_Manager(obj, Path, value, Action, strict)
{
try
{
if(Array.isArray(Path) == false)
{
Path = [Path];
}
let level = 0;
var Return_Value;
Path.reduce((a, b)=>{
console.log(level,':',a, '|||',b)
if (!strict){
if (!(b in a)) a[b] = {}
}
level++;
if (level === Path.length)
{
if(Action === 'Set')
{
a[b] = value;
return value;
}
else if(Action === 'Get')
{
Return_Value = a[b];
}
else if(Action === 'Unset')
{
delete a[b];
}
}
else
{
return a[b];
}
}, obj);
return Return_Value;
}
catch(err)
{
console.error(err);
return obj;
}
}
Example
obja = {
"a": {
"b":"nom"
}
}
// Set
path = "c.b" // Path does not exist
Object_Manager(obja,path.split('.'), 'test_new_val', 'Set', false);
// Expected Output: Object { a: Object { b: "nom" }, c: Object { b: "test_new_value" } }
来源：https://stackoverflow.com/questions/58881033/how-do-i-modify-a-nested-object-with-an-unknown-number-of-object-keys