Why splice method does not work and delete item on array in TypeScript

Question

I have an array type Person that has some data. Example:

const people = [{name: "John", age: "18"},{name: "Mike", content: "20"},{label: "Brand", content: "18"},{label: "Alice", content: "50"},{label: "Zina", content: "10"}];

I have another array type of string[] that has the following data: names=["John", "Zina"];

I try to delete the names that are on the second array from the first array like this:

  for (let i = 0; i < people.length; i++) {
    for (let j = 0; j < names.length; j++) {
      if (names[j] === people[i].name) {
        people.splice(i);
      }
    }
  }

Why it does not work?

Why the sudden switch in the properties? Some have name while other have label.. — Murat Karagöz
– Murat Karagöz, Commented Feb 24, 2020 at 10:04
You are missing the second parameter to splice. It will delete all the items starting from i. Even if you change it to people.splice(i, 1), it will break the loop because: Looping through array and removing items, without breaking for loop. You need to loop in the reverse direction to make it work — adiga
– adiga, Commented Feb 24, 2020 at 10:05

adiga · Accepted Answer · 2020-02-24 10:20:00Z

2

If you like to keep the object reference from people, you could iterate people from the end, because Array#splice with items to delete changes the indices of the following items.

var people = [{ name: "Mike", content: "20" }, { label: "Brand", content: "18" }, { label: "Alice", content: "50" }, { label: "Zina", content: "10" }],
    names = ["John", "Zina"],
    i = people.length;

while (i--) {
    if (names.includes(people[i].name) || names.includes(people[i].label)) {
        people.splice(i, 1);
    }
}

console.log(people);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Feb 24, 2020 at 10:20

adiga

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answered Feb 24, 2020 at 10:09

Nina Scholz

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1 Comment

Kathrine Hanson Over a year ago

property includes does not exist on type string []

Mihai Alexandru-Ionut · Accepted Answer · 2020-02-24 10:04:38Z

1

The splice method is modifying the array inplace. I suggest you to use filter method.

const people = [{name: "John", age: "18"},{name: "Mike", content: "20"},{name: "Brand", content: "18"},{name: "Alice", content: "50"},{name: "Zina", content: "10"}], names=["John", "Zina"];


console.log(people.filter(({name}) => !names.includes(name)));

answered Feb 24, 2020 at 10:04

Mihai Alexandru-Ionut

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2 Comments

Kathrine Hanson Over a year ago

This does not work while names is a type of string array

Mihai Alexandru-Ionut Over a year ago

@KathrineHanson, then use indexOf instead includes

sunny singh · Accepted Answer · 2020-02-24 10:28:46Z

0

Splice is modifying the original array. i.e. on each iteration if condition return true, people array at that index gets replaced with undefined and hence gets error.

you can use slice method to get data that you want to delete.

 for (let i = 0; i < people.length; i++) {
    for (let j = 0; j < names.length; j++) {
      if (names[j] === people[i].name) {
     console.log("matched",names[j],people[i].name, people.slice(i,i+1),);
      }
    }
  }

or you can simply filter data using Filter method.

answered Feb 24, 2020 at 10:28

sunny singh

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Comments

Shiv Patne · Accepted Answer · 2020-02-24 10:10:34Z

0

Please refer below Code.

const people = [{name: "John", age: "18"},{name: "Mike", content: "20"},{label: "Brand", content: "18"},{label: "Alice", content: "50"},{label: "Zina", content: "10"}];
const names = ["Mike","Shiv"];

for (let i = 0; i < people.length; i++) {
debugger
    for (let j = 0; j < names.length; j++) {
      if (names[j] === people[i].name) {
        people.splice(i,1);
      }
    }
  }
 console.log(people)

answered Feb 24, 2020 at 10:10

Shiv Patne

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