Notes on Day 14 of 30 Days of JavaScript

• notes • series • javascript • javascript30

Table of Contents

Lessons Learned

Array.prototype.concat()

The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

const start = [1, 2, 3, 4, 5]
const end = [6, 7, 8, 9, 10]

start.concat(end)
> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

console.log(start)
> [1, 2, 3, 4, 5]

start.concat()
> [1, 2, 3, 4, 5]

Object.assign()

This method copies all enumerable own properties from one or more source objects to a target object. It returns the modified target object.

It has the following syntax:

Object.assign(<destination object>, <source object>, ...args)

Some examples:

const square = { sides: 4, color: 'blue' }
const rectangle = Object.assign({}, square, { perimeter: '2L + 2W' })

console.log(rectangle)
> {sides: 4, color: 'blue', perimeter: '2L + 2W'}

console.log(square)
> {sides: 4, color: 'blue'}

For deep copy, it is not recommended especially in React-Redux operations that need to handle complex states.

References

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