How do I turn an array of JavaScript objects into an URL string with only one loop?

Question

I am trying to turn an array of JavaScript objects into a URL string with params, as seen below:

const objects = [{
    firstName: "John",
    lastName: "Doe",
    age: 46
  },
  {
    country: "France",
    lastName: "Paris"
  }
]

let entry_arr = [];

objects.forEach(obj => {
  Object.entries(obj).forEach(entry => {
    entry_arr.push(entry.join('='));
  });
});

let entry_str = entry_arr.join('&');

console.log(entry_str);

By all appearances, the above code works. There is a problem though.

The problem

As you can see, I have 2 nested forEach loops. For better performance, I wish I knew how to avoid this nesting and instead use only one forEach loop.

How can I achieve the same result with inly one loop?

It is an array with objects containing multiple and different keys so you need two loops for this. If you make a structure which always have the same keys then you could do this with one loop. — nbjorling
– nbjorling, Commented Jan 9, 2023 at 10:28
Smells like Premature Optimisation. Are you calling this code frequently enough that it has a noticeable performance impact? — Quentin
– Quentin, Commented Jan 9, 2023 at 10:28
Note that your code fails to escape any special characters that might be in your data. Using URLSearchParams would be more robust. — Quentin
– Quentin, Commented Jan 9, 2023 at 10:32
You could use: new URLSearchParams(Object.assign({}, ...objects)).toString(). But, this will overwrite the duplicate parameter lastName. This will also handle special characters in values. — adiga
– adiga, Commented Jan 9, 2023 at 10:51

Juljo Shahini · Accepted Answer · 2023-01-09 11:01:16Z

2

Merging each object inside the array in a main one would be the only solution I can think of. ( I assumed lastName: paris was a typo)

const objects = [{
    firstName: "John",
    lastName: "Doe",
    age: 46
  },
  {
    country: "France",
    city: "Paris"
  }
]

const obj = objects.reduce((acc, obj) => Object.assign(acc, obj), {});

const entry_str = Object.entries(obj).map(entry => 
    entry.join('=')
  ).join('&');

console.log(entry_str);

edited Jan 9, 2023 at 11:01

answered Jan 9, 2023 at 10:38

Juljo Shahini

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Comments

Fiodar Shurankou · Accepted Answer · 2023-01-09 12:59:26Z

1

The answer provided by Nina stil uses a nested loop, instead of using forEach, map is used.

For special character handling i strongly recommend to use the URLSearchParams class.

I would advise to join the array of objects in one single objects with reduce and import the entries in a URLSearchParams

const objects = [
    { firstName: "John", lastName: "Doe", age: 46 }, { country: "France", lastName: "Paris" }];
let reduced = objects.reduce((acc, object) => Object.assign(acc, object))
let params = new URLSearchParams(reduced);

console.log(reduced);
console.log(params.toString());

answered Jan 9, 2023 at 12:59

Fiodar Shurankou

257 bronze badges

Comments

Nina Scholz · Accepted Answer · 2023-01-09 10:53:12Z

0

At least, you need to map the entries with joining key and value and join the nested entries and outer array.

const
    objects = [{ firstName: "John", lastName: "Doe", age: 46 }, { country: "France", lastName: "Paris" }],
    result = objects
        .map(object => Object
            .entries(object)
            .map(entry => entry.join('='))
            .join('&')
        )
        .join('&');

console.log(result);

edited Jan 9, 2023 at 10:53

answered Jan 9, 2023 at 10:30

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

2 Comments

Razvan Zamfir Over a year ago

There is a problem though: the ampersand character (&) is converted to %26 when I do a GET request. (I use the params as HttpParams in Angular).

Nina Scholz Over a year ago

i am sorry, i have no clue of angular.. maybe angular allowes to add key value pairs as parameters.

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