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javascript equivalent to [x for x in array]

Is there any operation in Javascript just like [x for x in array] in python?
For example, I'm using javascript to reading a json file where there're dozens of (key, value) pairs needed to be handled(or transformed into other format). And I thought working in this way is stupid:
let transformed = []
for (let key in json){
transformed = [ /* doing some transform*/ ]
}
Is there anything like:
let transformed = [
lambda function1(key), lambda function2(value) for key, value in json
]
Thanks in advance.

The rough equivalent of Python's list comprehension is Array.map:
const myArray = [1, 2, 3]
const transformed = myArray.map((item) => item + 1)
// [2, 3, 4]
But your example is not about an array, but about an Object with keys and values. In Python, this would be a dict, and you'd use a dict comprehension along the lines of {function1(key): function2(value) for key, value in my_dict.items()}.
In JavaScript, you can turn such an object into an array with Object.entries, then perform the map, and finally transform it back into an object using Object.fromEntries:
const myObject = { a: 1, b: 2 }
const transformed = Object.fromEntries(Object.entries(myObject)
.map(([key, value]) => [key + 'x', value + 1]))
// { ax: 2, bx: 3 }
Note that fromEntries is fairly new and you might need to add a polyfill for it.

You can use a code likes this. You must use a function that handle operation on current single item.
const words = ['hello', 'bird', 'table', 'football', 'pipe', 'code'];
const capWords = words.forEach(capitalize);
function capitalize(word, index, arr) {
arr[index] = word[0].toUpperCase() + word.substring(1);
}
console.log(words);
// Expected output:
// ["Hello", "Bird", "Table", "Football", "Pipe", "Code"]

First of all, javascript does NOT support Associative Arrays. If you are used to them in Python, PHP, and other languages you need to do a little workaround in JS to achieve the same functionality.
The most common way to simulate an associative array is using an object.
let testObject = {name: "Color", value: "Red"};
And then you push every object into an array so you end up with something like this:
let testArray = [{name: "Color", value: "Red"}, {name: "Color", value: "Blue"}];
Once you have this array consisting of objects, you can use map function to go through every object in the array and do whatever you want with it.
testArray.map((item, index) => {
console.log("The value of "+index+". item is: "item.value);
})

You can use Array.map() function. It work pretty like Array.forEach() function
const numbers = [1, 2, 3, 4, 5]
let newArray = numbers.map((element) => {
return element * 2
})
console.log(newArray) // excepted : [ 2, 4, 6, 8, 10 ]
It can be reduce using
const numbers = [1, 2, 3, 4, 5]
let newArray = numbers.map(element => element * 2)
console.log(newArray) // excepted : [ 2, 4, 6, 8, 10 ]
For more informations, you can this documentation https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Javascript: select array into new array (like C# Select)

In C# if I had a list for example of 3 ints [1,2,3], I could trasform that list into another with .Select in following way [1,2,3].Select(e => new { Id = e, Name = $"name:{e}"), which would return new array with 3 objects.
how can I get the same result in js without using for loop?

You can use the map function like this:
var array = [1,2,3]
var result = array.map(e => ({id: e, name: `name:${e}`}))
console.log(result)
It returns the following result:
[ { id: 1, name: 'name:1' },
{ id: 2, name: 'name:2' },
{ id: 3, name: 'name:3' } ]
Here is the map function docs:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Yes, it is called map(example with integers, but you can map into objects too):
const array1 = [1, 4, 9, 16];
const map1 = array1.map(x => x * 2);
console.log(map1);
// expected output: Array [2, 8, 18, 32]

JavaScript: Find in array all values with substrings of array

I have two arrays; one with substrings and the other with objects.
I would like to obtain an array of objects where those objects contain any of the substrings in the substrings array.
So far I have tried to use filter and findIndex. Each approach works if a substring is identical. In this case, even indexOf was not working. I am not javascript guy, so probably I am doing something wrong.
Script
var strings = ['12', 'sv', 'eli', '23', '34'];
var data = [
{
a: 349531284734,
b: "sv123eippppppeli",
c: "aaabbbccc"
},
{
a: 1111123333312,
b: "ccccccccccccs2222",
c: "aaabbbccc"
},
{
a: 2222234,
b: "elllllllla",
c: false
},
];
// attempt 1
var results = data.filter(arr =>
Object.keys(arr).some(key => {
return String(arr[key]).toLowerCase().includes(strings) // or indexOf
})
);
// attempt 2 with only one data index
var obj = Object.values(data[0]);
var results = strings.some(s => obj.includes(s)) // or indexOf or findIndex;
Explanation
In this example with the given substrings, only data[0] is a match because it contains at least on of the substrings in the strings array.
How can I make this work without using a "for loop"?
Thanks

A simple solution that avoids the need for "for-loop" syntax would be to filter() each object of data by a predicate that checks if any value (of the current item being filtered) contains any one of the values of the strings array.
In code, this can be expressed as:
var strings = ['12', 'sv', 'eli', '23', '34'];
var data = [{
a: 349531284734,
b: "sv123eippppppeli",
c: "aaabbbccc"
},
{
a: 1111123333312,
b: "ccccccccccccs2222",
c: "aaabbbccc"
},
{
a: 2222234,
b: "elllllllla",
c: false
},
];
// Local helper retruns true if case-insenstive value in strings array
const stringHasValue = (value) => strings
.some(str => value.toLowerCase().includes(str.toLowerCase()))
// Filter each item in data array by existance of a value containing
// substring in strings array
var result = data.filter((item) => Object.values(item)
.filter(value => typeof value === 'string')
.some(stringHasValue, []));
console.log(result);

Trouble using javascript partial.lenses to obtain properties within an array

I'm trying to figure out how to create a lens that'll give me an array of the key values from within an array. Here's a simple example:
const L = require('partial.lenses');
const data = [
{
r: [
{
d: {
one: 1,
two: 2
}
}
]
},
{
r: [
{
d: {
three: 3,
four: 4
}
}
]
}
];
const lens = L.compose (
L.elems,
L.prop ('r'),
L.elems,
L.prop ('d'),
);
const result = L.get (lens, data);
console.log (result);
I want:
[{ one: 1, two: 2 }, { three: 3, four: 4 }]
But get:
{ one: 1, two: 2 }
I'm sure this is trivial, but can't get it quite right. Once my lens correctly selects the array of 'd's I want to use L.modify to get the data with all of the 'd' objects replaced with a string. I think I know how to do once my lens is correct.
Thanks

Use L.collect instead of L.get, L.get returns the first found entity, while L.collect returns all matching entities, similar to [].filter vs [].find.
https://github.com/calmm-js/partial.lenses#l-collect

Parse.com retrieving value of nested object

Lets say i have object like this:
var a = {
b: {
c: 1,
d: 2
}
}
And i have saved this object in Parse backend. There are 100 objects, but with different c and d values. Can i do search searching only objects which contains d:2. Or the only way is to query all objects and then use for loop which will search for d:2?
Dont read this!
Writting this line just to get posted, because system does not allow to post me question, dont know why
Thank you
Update
Maybe i am not clear enough, I am using parse.com you can retrieve objects by using this line:
var GameScore = Parse.Object.extend("GameScore");
var query = new Parse.Query(GameScore);
query.equalTo("playerName", "Dan Stemkoski");
query.find();
If anybody knows if you can retrieve objects with specific values in nested objects, that would be great.

You can do something like this
var a = {
b0: {
c: 1,
d: 2
},
b1: {
c: 5,
d: 3
},
b2: {
c: 1,
d: 4
},
b3: {
c: 2,
d: 2
},
b4: {
c: 1,
d: 4
},
b5: {
c: 7,
d: 2
},
},
d2s = Object.keys(a).filter(e => a[e].d == 2).map(e => a[e]);
document.write("<pre>" + JSON.stringify(d2s,null,2) + "</pre>");