JAVASCRIPT.md

Awesome JavaScript Tips

Contents

• Shorten an array
• Short-circuits conditionals
• Assigning the remaining part of an array
• Object property assigning to a variable with a different name
• Select a subset of columns to display when doing console.table()
• Remove duplicate elements from the array
• Remove all falsy values from an array
• Convert a number to string
• Convert a numeric string to number
• Calculate the sum of all elements in array
• Use template literals to concatenate strings
• Get the maximum of an array
• Transform the array elements using the map function
• Calculate the running sum of an array with currying

Shorten an array

You can set the length property to shorten an array.

const numbers = [1, 2, 3, 4, 5];

numbers.length = 3;

console.log(numbers); // Array(3) [1, 2, 3]

Short-circuits conditionals

If you have to execute a function only if condition is true, you can use short-circuit.

// Instead of this
if (condition) {
    doSomething();
}

// You can use short-circuit
condition && doSomething();

Assigning the remaining part of an array

When destructuring an array, you can unpack and assign the remaining part of it to a variable using the rest pattern:

const [a, ...b] = [1, 2, 3, 4, 5];
console.log(a); // 1
console.log(b); // [2, 3, 4, 5]

Object property assigning to a variable with a different name

A property can be unpacked from an object and assigned to a variable with a different name than the object property:

const obj = {a: 42, b: true};
const {a: foo, b: bar} = obj;
console.log(foo); // 42
console.log(bar); // true

Select a subset of columns to display when doing console.table()

By default, console.table() lists all elements in each row. You can use the optional "columns" parameter to select a subset of columns to display:

// an array of objects, logging only firstName
function Person(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
}

const john = new Person("John", "Smith");
const jane = new Person("Jane", "Doe");

console.table([john, jane], ["firstName"]);

Remove duplicate elements from the array

const myArray = [5, 4, 3, 'a', 5, 5, 'a'];
console.log([... new Set(myArray)]); // [5, 4, 3, "a"]

Remove all falsy values from an array

const myArray = [1, undefined, NaN, 2, null, '@denicmarko', true, 3, false];
console.log(myArray.filter(Boolean)); // [1, 2, '@denicmarko', true, 3]

Convert a number to string

const number = 403;
console.log(number + ''); // '403'

Convert a numeric string to number

const numericString = '403';
console.log(+ numericString); // 403

Calculate the sum of all elements in array

You can use reduce method to calculate the sum of all elements in array:

const myArray = [10, 20, 30, 40];
const reducer = (total, currentValue) => total + currentValue;
console.log(myArray.reduce(reducer)); // 100

Use template literals to concatenate strings

let name = 'Horse';
console.log(`The ${name} is sleeping`); // the Horse is sleeping 

Get the maximum of an array

let arr = [3, 5, 1];
console.log(Math.max(...arr)); // 5

Transform the array elements using the map function

const myArray = [1,2,3,4];

console.log(myArray.map(value => value * 2)); // [2, 4, 6, 8]

Calculate the running sum of an array with currying

Here, a function is called with the initial sum value of zero that returns a function which accumulates the values of myArray.

const myArray = [1,1,1,1];

console.log(myArray.map((sum => value => sum += value)(0))); // [1, 2, 3, 4]