'How to iterate over a JavaScript object?
I have an object in JavaScript:
{
abc: '...',
bca: '...',
zzz: '...',
xxx: '...',
ccc: '...',
// ...
}
I want to use a for loop to get its properties. And I want to iterate it in parts (not all object properties at once).
With a simple array I can do it with a standard for loop:
for (i = 0; i < 100; i++) { ... } // first part
for (i = 100; i < 300; i++) { ... } // second
for (i = 300; i < arr.length; i++) { ... } // last
But how to do it with objects?
Solution 1:[1]
Here is another iteration solution for modern browsers:
Object.keys(obj)
.filter((k, i) => i >= 100 && i < 300)
.forEach(k => console.log(obj[k]));
Or without the filter function:
Object.keys(obj).forEach((k, i) => {
if (i >= 100 && i < 300) {
console.log(obj[k]);
}
});
However you must consider that properties in JavaScript object are not sorted, i.e. have no order.
Solution 2:[2]
Using Object.entries you do something like this.
// array like object with random key ordering
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(anObj)); // [ ['2', 'b'],['7', 'c'],['100', 'a'] ]
The Object.entries() method returns an array of a given object's own enumerable property [key, value]
So you can iterate over the Object and have key and value for each of the object and get something like this.
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
Object.entries(anObj).map(obj => {
const key = obj[0];
const value = obj[1];
// do whatever you want with those values.
});
or like this
// Or, using array extras
Object.entries(obj).forEach(([key, value]) => {
console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});
For a reference have a look at the MDN docs for Object Entries
Solution 3:[3]
With the new ES6/ES2015 features, you don't have to use an object anymore to iterate over a hash. You can use a Map. Javascript Maps keep keys in insertion order, meaning you can iterate over them without having to check the hasOwnProperty, which was always really a hack.
Iterate over a map:
var myMap = new Map();
myMap.set(0, "zero");
myMap.set(1, "one");
for (var [key, value] of myMap) {
console.log(key + " = " + value);
}
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
for (var key of myMap.keys()) {
console.log(key);
}
// Will show 2 logs; first with "0" and second with "1"
for (var value of myMap.values()) {
console.log(value);
}
// Will show 2 logs; first with "zero" and second with "one"
for (var [key, value] of myMap.entries()) {
console.log(key + " = " + value);
}
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
or use forEach:
myMap.forEach(function(value, key) {
console.log(key + " = " + value);
}, myMap)
// Will show 2 logs; first with "0 = zero" and second with "1 = one"
Solution 4:[4]
If you want the key and value when iterating, you can use a for...of loop with Object.entries.
const myObj = {a: 1, b: 2}
for (let [key, value] of Object.entries(myObj)) {
console.log(`key=${key} value=${value}`)
}
// output:
// key=a value=1
// key=b value=2
Solution 5:[5]
The only reliable way to do this would be to save your object data to 2 arrays, one of keys, and one for the data:
var keys = [];
var data = [];
for (var key in obj) {
if (obj.hasOwnProperty(key)) {
keys.push(key);
data.push(obj[key]); // Not necessary, but cleaner, in my opinion. See the example below.
}
}
You can then iterate over the arrays like you normally would:
for(var i = 0; i < 100; i++){
console.log(keys[i], data[i]);
//or
console.log(keys[i], obj[keys[i]]); // harder to read, I think.
}
for(var i = 100; i < 300; i++){
console.log(keys[i], data[i]);
}
I am not using Object.keys(obj), because that's IE 9+.
Solution 6:[6]
->if we iterate over a JavaScript object using and find key of array of objects
Object.keys(Array).forEach(key => {
console.log('key',key)
})
Solution 7:[7]
If you have a simple object you can iterate through it using the following code:
let myObj = {
abc: '...',
bca: '...',
zzz: '...',
xxx: '...',
ccc: '...',
// ...
};
let objKeys = Object.keys(myObj);
//Now we can use objKeys to iterate over myObj
for (item of objKeys) {
//this will print out the keys
console.log('key:', item);
//this will print out the values
console.log('value:', myObj[item]);
}If you have a nested object you can iterate through it using the following code:
let b = {
one: {
a: 1,
b: 2,
c: 3
},
two: {
a: 4,
b: 5,
c: 6
},
three: {
a: 7,
b: 8,
c: 9
}
};
let myKeys = Object.keys(b);
for (item of myKeys) {
//print the key
console.log('Key', item)
//print the value (which will be another object)
console.log('Value', b[item])
//print the nested value
console.log('Nested value', b[item]['a'])
}If you have array of objects you can iterate through it using the following code:
let c = [
{
a: 1,
b: 2
},
{
a: 3,
b: 4
}
];
for(item of c){
//print the whole object individually
console.log('object', item);
//print the value inside the object
console.log('value', item['a']);
}Solution 8:[8]
const o = {
name: "Max",
location: "London"
};
for (const [key, value] of Object.entries(o)) {
console.log(`${key}: ${value}`);
}
Solution 9:[9]
If you wanted to iterate the whole object at once you could use for in loop:
for (var i in obj) {
...
}
But if you want to divide the object into parts in fact you cannot. There's no guarantee that properties in the object are in any specified order. Therefore, I can think of two solutions.
First of them is to "remove" already read properties:
var i = 0;
for (var key in obj) {
console.log(obj[key]);
delete obj[key];
if ( ++i > 300) break;
}
Another solution I can think of is to use Array of Arrays instead of the object:
var obj = [['key1', 'value1'], ['key2', 'value2']];
Then, standard for loop will work.
Solution 10:[10]
I finally came up with a handy utility function with a unified interface to iterate Objects, Strings, Arrays, TypedArrays, Maps, Sets, (any Iterables).
const iterate = require('@a-z/iterate-it');
const obj = { a: 1, b: 2, c: 3 };
iterate(obj, (value, key) => console.log(key, value));
// a 1
// b 2
// c 3
Solution 11:[11]
For object iteration we usually use a for..in loop. This structure will loop through all enumerable properties, including ones who are inherited via prototypal inheritance. For example:
let obj = {
prop1: '1',
prop2: '2'
}
for(let el in obj) {
console.log(el);
console.log(obj[el]);
}However, for..in will loop over all enumerable elements and this will not able us to split the iteration in chunks. To achieve this we can use the built in Object.keys() function to retrieve all the keys of an object in an array. We then can split up the iteration into multiple for loops and access the properties using the keys array. For example:
let obj = {
prop1: '1',
prop2: '2',
prop3: '3',
prop4: '4',
};
const keys = Object.keys(obj);
console.log(keys);
for (let i = 0; i < 2; i++) {
console.log(obj[keys[i]]);
}
for (let i = 2; i < 4; i++) {
console.log(obj[keys[i]]);
}Solution 12:[12]
Yes. You can loop through an object using for loop. Here is an example
var myObj = {
abc: 'ABC',
bca: 'BCA',
zzz: 'ZZZ',
xxx: 'XXX',
ccc: 'CCC',
}
var k = Object.keys (myObj);
for (var i = 0; i < k.length; i++) {
console.log (k[i] + ": " + myObj[k[i]]);
}NOTE: the example mentioned above will only work in IE9+. See Objec.keys browser support here.
Solution 13:[13]
<script type="text/javascript">
// method 1
var images = {};
images['name'] = {};
images['family'] = {};
images[1] = {};
images['name'][5] = "Mehdi";
images['family'][8] = "Mohammadpour";
images['family']['ok'] = 123456;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][22] = 2602;
images[1][23] = 2602;
for (const [key1, value1] of Object.entries(images)){
for (const [key2, value2] of Object.entries(value1)){
console.log(`${key1} => ${key2}: ${value2}`);
}
}
console.log("=============================");
// method 2
var arr = [];
for(var x = 0; x < 5; x++){
arr[x] = [];
for(var y = 0; y < 5; y++){
arr[x][y] = x*y;
}
}
for(var i = 0; i < arr.length; i++) {
var cube = arr[i];
for(var j = 0; j < cube.length; j++) {
console.log("cube[" + i + "][" + j + "] = " + cube[j]);
}
}
</script>
Solution 14:[14]
var Dictionary = {
If: {
you: {
can: '',
make: ''
},
sense: ''
},
of: {
the: {
sentence: {
it: '',
worked: ''
}
}
}
};
function Iterate(obj) {
for (prop in obj) {
if (obj.hasOwnProperty(prop) && isNaN(prop)) {
console.log(prop + ': ' + obj[prop]);
Iterate(obj[prop]);
}
}
}
Iterate(Dictionary);
Solution 15:[15]
You can try using lodash- A modern JavaScript utility library delivering modularity, performance & extras js to fast object iterate:-
var users = {
'fred': {
'user': 'fred',
'age': 40
},
'pebbles': {
'user': 'pebbles',
'age': 1
}
};
_.mapValues(users, function(o) {
return o.age;
});
// => { 'fred': 40, 'pebbles': 1 } (iteration order is not guaranteed)
// The `_.property` iteratee shorthand.
console.log(_.mapValues(users, 'age')); // returns age property & value
console.log(_.mapValues(users, 'user')); // returns user property & value
console.log(_.mapValues(users)); // returns all objects
// => { 'fred': 40, 'pebbles': 1 } (iteration order is not guaranteed)<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash-compat/3.10.2/lodash.js"></script>Solution 16:[16]
Really a PITA this is not part of standard Javascript.
/**
* Iterates the keys and values of an object. Object.keys is used to extract the keys.
* @param object The object to iterate
* @param fn (value,key)=>{}
*/
function objectForEach(object, fn) {
Object.keys(object).forEach(key => {
fn(object[key],key, object)
})
}
Note: I switched the callback parameters to (value,key) and added a third object to make the API consistent other APIs.
Use it like this
const o = {a:1, b:true};
objectForEach(o, (value, key, obj)=>{
// do something
});
Solution 17:[17]
Here is a Hand Made Solution:
function iterationForObject() {
let base = 0,
Keys= Object.keys(this);
return {
next: () => {
return {
value: {
"key": Keys[base],
"value": this[Keys[base]]
},
done: !(base++ < Keys.length)
};
}
};
}
Object.prototype[Symbol.iterator] = iterationForObject;
And Then You Can Loop Any Object:
for ( let keyAndValuePair of (Object Here) ) {
console.log(`${keyAndValuePair.key} => ${keyAndValuePair.value}`);
}
Solution 18:[18]
There are a number of syntax choices but this one defines the structure upfront (in the signature) and thus eliminates the need for selectors or subscripts to access any part of the object. k is key, v is value, i is index.
const obj = {
kiwi: true,
mango: false,
pineapple: 500
};
Object.entries(obj).forEach(([k, v], i) => {
console.log(k, v, i);
});
// kiwi true 0
// mango false 1
// pineapple 500 2
Sources
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Source: Stack Overflow