concatenate Objects data in one string

Question

I have a table that contains objects in JSON:

    items=[
      {"label":"180","quantity":10},
      {"label":"50","quantity":35},
      {"label":"80","quantity":15},
      {"label":"180","quantity":120},
   ]

label is a string and quantity is a number, and every time user click on Add button a newItem is added to this table + {"label":"80","quantity":11}

what I want is to concatenate this data into one string like this: str == '180_10,50_35,80_15,180_120'

and when user click on Add str will be : str == '180_10,50_35,80_15,180_120,80_11' (with new item added 80_11)

my approach doesn't work :

  addRecup = () => {
    const newItem = {
      label: this.state.values[this.state.codeValue-1].label,
      quantity: this.state.quantite
    };
    this.setState(state => ({
      items: state.items.concat([newItem]), // add new item, it works
    }));

    let str = '';
    let concat = this.state.items.map((item,key) => (
      str = str + ',' + this.state.items.label + ',' + this.state.items.quantity // concatenate json doesn't work
    ));

    console.warn('str: ' + str); // got str: undefined,undefined,undefined...
  }

That's not [JSON](http://json.org) -> [What is the difference between JSON and Object Literal Notation?](https://stackoverflow.com/questions/2904131/what-is-the-difference-between-json-and-object-literal-notation) — Andreas, Dec 07 '19 at 10:52

score 2 · Accepted Answer · answered Dec 07 '19 at 10:54

2

Using map() and join()

let items=[
  {"label":"180","quantity":10},
  {"label":"50","quantity":35},
  {"label":"80","quantity":15},
  {"label":"180","quantity":120},
]

let res = items.map(v => Object.values(v).join('_')).join(',')

console.log(res)

answered Dec 07 '19 at 10:54

User863

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thank you it works good but just a little issue : when I console.log it I have always an item missing, this missed item is shown next time when I click Add button. I explain more if I have 4 object in item[] I most have res variable contains this 4 object concatenated but there is only 3 – zedArt Dec 07 '19 at 11:14
@zedArt the issue you are mentioning is something not related to this answer. please check https://stackoverflow.com/questions/36085726/why-is-setstate-in-reactjs-async-instead-of-sync – User863 Dec 07 '19 at 11:23
@zedArt solution available in answer https://stackoverflow.com/a/40408976/8053274 – User863 Dec 07 '19 at 13:36

Pranav C Balan · Answer 2 · 2019-12-07T11:39:04.587

You can use Array#map method to generate array of _ separated values and then use Array#join to combine them.

const items = [{"label":"180","quantity":10},{"label":"50","quantity":35},{"label":"80","quantity":15},{"label":"180","quantity":120}];

console.log(items.map(v => `${v.label}_${v.quantity}`).join(','))

Or use Array#reduce method to do the same thing by concatenating string.

const items = [{"label":"180","quantity":10},{"label":"50","quantity":35},{"label":"80","quantity":15},{"label":"180","quantity":120}]; 

console.log(items.reduce((str, v, i) => str + `${i? ',' : ''}${v.label}_${v.quantity}`, ''))

concatenate Objects data in one string

2 Answers2