help me please. There are 2 arrays, one with objects of the other numeric. Numeric stores the number from the array with the objects.

How can I find the index of an object using a numeric array and change the selected: true object?

Now a newArr happens to newArr , but arr itself changes the value of the selected

 var arr = [{ name: 'Hello', selected: false, number: 14 }, { name: 'World', selected: false, number: 18 }, { name: '!', selected: false, number: 31 }] var numbers = [14, 31]; var newArr = arr.map((item, index) => numbers.map((number) => item.number == number ? arr[index].selected = true : arr[index])) console.log(newArr)

    2 answers 2

    Here you need to understand a few things:

    • map receives an array as input and returns a new array.
    • if an element of the original array was an object, then it will be passed by reference (that is, item and arr [index] are the same object)
    • The arrow function in the nonblock form returns the result of the last operation.

    Miracles became possible because the basic features of the map and turnout functions were not taken into account. Well, it is clearly not an effective solution to iterate through the numbers array for each element of the arr array.

    From the question it is not clear which one you want to get the result on; I will demonstrate 3 (more efficient) options:

    • change selected to arr
    • create newArr from arr array objects
    • create newArr from copies of arr objects.

    Go!

    Change selected to arr :

     var arr = [{name: 'Hello', number: 14}, {name: 'World', number: 18}, {name: '!', number: 31}]; var numbers = [14, 31]; arr.forEach(x => x.selected = numbers.indexOf(x.number) > -1); console.log(arr);

    Create newArr from the arr array objects :

     var arr = [{name: 'Hello', number: 14}, {name: 'World', number: 18}, {name: '!', number: 31}]; var numbers = [14, 31]; var newArr = arr.map(x => { x.selected = numbers.indexOf(x.number) > -1; return x; }); console.log(newArr); console.log(arr);

    Create a newArr from copies of arr objects :

     var arr = [{name: 'Hello', number: 14}, {name: 'World', number: 18}, {name: '!', number: 31}]; var numbers = [14, 31]; var newArr1 = arr.map(x => { var o = Object.assign({}, x); o.selected = numbers.indexOf(o.number) > -1; return o; }); var newArr2 = arr.map(x => Object.assign({selected: (numbers.indexOf(x.number) > -1)}, x)); var newArr3 = arr.map(x => { return { ...x , selected: (numbers.indexOf(x.number) > -1) }; }); console.log(newArr2); console.log(arr);

    • My example returns the data in newArr - Puvvl
    • @Puvvl, I wrote the answer on the road and am going to expand it now - nörbörnën
    • @Puvvl now ask your answers - nörbörnën
    • 2nd option is very good. Would numbers.indexOf(o.number) > -1 to numbers.includes(o.number) . Thanks for the detailed answer. - Puvvl

    In this way:

     var arr = [{ name: 'Hello', selected: false, number: 14 }, { name: 'World', selected: false, number: 18 }, { name: '!', selected: false, number: 31 }] var numbers = [14, 31]; var newArr = arr.map((item, index) => { numbers.map((number) => { if (item.number == number) arr[index].selected = true; return arr[index];}); return item;} ); console.log(newArr)