Create a string using forEach in javascript

Question

So I have an array of strings like this:

myData = ["111", "222", "333"]

I want to build a string having this structure:

"{
 "111" : [{"type" : "line"}],
 "222" : [{"type" : "line"}],
 "333" : [{"type" : "line"}],
}"

Basically, for each element in array to add that type and line which are the same for all, and put it inside curly brackets, all this being a string.

This is my unsuccessful approach until now:

let result ="{";
myData.forEach(
    result = result + '"' + baselineTitle + '" [{"type":"line"}]'; 
);
result = result + "}"

Do you happen to want to create a JSON string…? Then create an object according to your desired format and JSON.stringify it. — deceze
– deceze ♦, Commented Nov 21, 2017 at 15:13
Never create json manually. It is error prone and more work than creating objects/arrays and serializing them — charlietfl
– charlietfl, Commented Nov 21, 2017 at 15:14

Orelsanpls · Accepted Answer · 2017-11-21 16:12:41Z

3

I agree with @deceze about using JSON.stringify, here is an example :

const object = ['111', '222', '333'].reduce((tmp, x) => {
  tmp[x] = [{
    type: 'line',
  }];
  
  return tmp;
}, {});

console.log(JSON.stringify(object, null, 2));

You will notice the use of Array.reduce which is the most adequate method to use in here.

EDIT about ptr

EDIT 2 about ptr

It's better to disable the eslint no-param-reassign rule

edited Nov 21, 2017 at 16:12

answered Nov 21, 2017 at 15:15

Orelsanpls

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11 Comments

Roland Starke Over a year ago

Is there a need for the ptr variable?

Orelsanpls Over a year ago

It's a bad practice to modify a function parameter. At least in the style guide I use airbnb. They say

Why? Reassigning parameters can lead to unexpected behavior, especially when accessing the arguments object. It can also cause optimization issues, especially in V8.

.

deceze Over a year ago

I would regard ptr as somewhat academic in this case. In general no-param-reassign is not wrong, but there's little technical reason to obey it here. It would make the code more concise to disregard it here. I don't think the engine optimisations which may or may not happen here make a big difference either way. At least you'd have to benchmark it.

Roland Starke Over a year ago

Looks like there is already a discussion on the usefullness: github.com/eslint/eslint/issues/5306

Roland Starke Over a year ago

"I would never expect (nor have I ever seen) someone bypass this linter rule (no-param-manipulation) with your second example (reassigning the param variable)" :D

|

Nina Scholz · Accepted Answer · 2017-11-21 15:21:30Z

2

You could generate the object first and then get a stringified version of it.

var array = ["111", "222", "333"],
    object = Object.assign(...array.map(k => ({ [k]: [{ type: "line" }] }))),
    json = JSON.stringify(object);

console.log(json);
console.log(object);

answered Nov 21, 2017 at 15:21

Nina Scholz

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Comments

SatansDeer · Accepted Answer · 2017-11-21 15:38:45Z

2

As I understood you want to get JSON here.

I would use JSON.stringify() instead of generating it manually. Also I would use reduce method instead of forEach.

const myData = ['111', '222', '333'];

const result = JSON.stringify(myData.reduce(function(accumulator, currentValue){
    accumulator[currentValue] = [{type: 'line'}];
    return accumulator;
}, {}));

console.log(result);

edited Nov 21, 2017 at 15:38

answered Nov 21, 2017 at 15:24

SatansDeer

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Comments

Ivan Demidov · Accepted Answer · 2017-11-21 15:20:26Z

1

use reduce.

const result = ["111", "222", "333"].reduce((prev, curr) => Object.assign(prev, {[curr]: [{type:'line'}]}), {});


console.log(result);

answered Nov 21, 2017 at 15:20

Ivan Demidov

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Comments

Jonas Mendes · Accepted Answer · 2017-11-24 19:27:54Z

1

You can use reduce to transform an array into an object like this:

const data = ['111', '222', '333'];

const result = data.reduce((acc, value) => (
  {
    ...acc,
    [`${value}`]: [{type: 'line'}]
  }
), {});

console.log(JSON.stringify(result));

And I decided to use pure stateless functional programming for the reduce case (without modifying any scope variable).

answered Nov 24, 2017 at 19:27

Jonas Mendes

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Geeky · Accepted Answer · 2017-11-21 15:14:55Z

0

Check the following snippet

const myData = ["111", "222", "333"]
const result = {}
for( const item of myData) {
  result[item]=[];
  result[item].push({"type" : "line"});
}

console.log(result)

answered Nov 21, 2017 at 15:14

Geeky

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1 Comment

deceze Over a year ago

result[item] = [{type: 'line'}];…

MRousse · Accepted Answer · 2017-11-21 15:16:02Z

0

The forEach loop takes a function as argument, you did not specify arguments and the function itself, a solution would be like this :

let result ="{";
myData.forEach((baselineTitle) => {
    result = result + '"' + baselineTitle + '" [{"type":"line"}]'; 
});
result = result + "}"

answered Nov 21, 2017 at 15:16

MRousse

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