Author: John Au-Yeung

To find first element of array matching a boolean condition in JavaScript, we use the find method.

For instance, we write

const result = someArray.find(isNotNullNorUndefined);

to call someArray.find with the isNotNullNorUndefined function which returns the boolean condition we’re looking for.

The first item with the condition if it’s found.

To change value of object which is inside an array using JavaScript, we use findIndex to find the item.

For instance, we write

const myArray = [
  { id: 0, name: "John" },
  { id: 1, name: "Sara" },
  { id: 2, name: "Domnic" },
  { id: 3, name: "Bravo" },
];

const objIndex = myArray.findIndex((obj) => obj.id == 1);
myArray[objIndex].name = "Bob";

to call findIndex to find index of the object in myArray with id 1.

Then we use the index to get the item from myArray and assign its name property to 'Bob'.

To perform .join on value in array of objects with JavaScript, we use map to map the array of object to an array of primitive values.

For instance, we write

const users = [
  { name: "Joe", age: 22 },
  { name: "Kevin", age: 24 },
  { name: "Peter", age: 21 },
];
const s = users.map((u) => u.name).join(", ");

to call users.map with a callback that gets the name property value from each object and return them in an array.

Then we call join to combine then into a string with commas.

To remove all elements contained in another array with JavaScript, we use the filter and includes method.

For instance, we write

const myArray = ["a", "b", "c", "d", "e", "f", "g"];
const toRemove = ["b", "c", "g"];
const newArray = myArray.filter((el) => {
  return !toRemove.includes(el);
});

to call myArray.filter with a callback that calls toRemove.includes with the el element being iterator through to return an array with the myArray entries that aren’t in toRemove.

To add an object to an array with JavaScript, we call the push method.

For instance, we write

const a = [];
const b = {};
a.push(b);

to call a.push with b to append b as the last element of a.