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.
To remove element from an array in JavaScript, we use the shift method.
For instance, we write
const array = [1, 2, 3, 4, 5];
array.shift();
to call array.shift to remove the first element of array in place.
To get the first element of an array with JavaScript, we use index 0.
For instance, we write
const array = ["first", "second", "third", "fourth", "fifth"];
alert(array[0]);
to get the first entry of array with array[0].