To add key value pair to all objects in array with JavaScript, we use the spread operator.
For instance, we write
const arr = [{ name: "eve" }, { name: "john" }, { name: "jane" }];
const newArr = arr.map((v) => ({ ...v, isActive: true }));
to call arr.map with a callback that returns an object with the properties in v spread into a new object.
And then we add the isActive property to the object.
To declare an empty two-dimensional array in JavaScript, we use the map method.
For instance, we write
const arr = [...Array(3)].map(() => Array(5));
to create an array with 3 empty slots with Array(3).
And then we spread them to a new array.
Then we call map with a callback that returns an array with 5 empty slots created with Array(5).
We now have a 3×5 empty 2d array.
To remove duplicate form an array with JavaScript, we can create a set.
For instance, we write
const array = [
{ id: 123, value: "value1", name: "Name1" },
{ id: 124, value: "value2", name: "Name1" },
{ id: 125, value: "value3", name: "Name2" },
{ id: 126, value: "value4", name: "Name2" },
];
const names = [...new Set(array.map((a) => a.name))];
console.log(names);
to call map to return an array of name property values from the objects in array.
Then we convert it to a set with the Set constructor.
Then we use the spread operator to convert the set into an array.
To split a JavaScript array into N arrays, we can use the splice method.
For instance, we write
const split = (array, n) => {
const [...arr] = array;
const res = [];
while (arr.length) {
res.push(arr.splice(0, n));
}
return res;
};
to define the split function.
In it, we make a copy of array with the rest operator.
And then we use a while loop that calls arr.splice to remove the items from index 0 to n - 1 from arr and return them in an array.
Then we call res.push to append the array into res.
This is done until arr is empty.
To loop through files in a folder with Node.js, we use the opendir method.
For instance, we write
const fs = require("fs");
const ls = async (path) => {
const dir = await fs.promises.opendir(path);
for await (const dirent of dir) {
console.log(dirent.name);
}
};
to call the opendir method with the folder path to return a promise with the items in the folder.
Then we use the for-await-of loop to loop through all the items in the folder.