Lists and Links

In Javascript, you want to create a new array from an available array by converting each element of the original array to create the corresponding element of the new array, you can use map() method.

##### For simplicity, please see the example, you have an array of integer numbers, such as [1, 2, 5], and you want to create another array by multiplying each element of the initial array by 10.

  var arr1 = [1, 2, 5];
 
console.log(arr1); // --> [1, 2, 5]
 
var arr2 = arr1.map( e  => e * 10 );
 
console.log(arr2); // --> [10, 20, 50]

2- React Keys

Keys helps React distinguish items in a list. It helps the React manage the changed items, new items added, or items removed from the list.

From an array of objects, you create a new array containing tags, which should have the key attribute, and their values are not allowed to be the same.

JS spread operator

Spread operator allows an iterable to expand in places where 0+ arguments are expected. It is mostly used in the variable array where there is more than 1 values are expected. It allows us the privilege to obtain a list of parameters from an array. Syntax of Spread operator is same as Rest parameter but it works completely opposite of it. thing can spread operator do!

• Copying an array.
• Concatenating or combining arrays.
• Using Math functions.
• Using an array as arguments.
• Adding an item to a list.
• Adding to state in React.
• Combining objects.
• Converting NodeList to an array.

merge two arrays 

let fruits = ["apples", "bananas"];
let vegetables = ["corn", "carrots"];
let produce = [...fruits, ...vegetables];
//["apples","bananas","corn","carrots"]

add to array:

var a = [1, 2, 3, 4, 5];
var b = [0].concat(a);

console.log(a);
console.log(b);

merge two objects 

let person = {
    firstName: 'John',
    lastName: 'Doe',
    age: 25,
    ssn: '123-456-2356'
};


let job = {
    jobTitle: 'JavaScript Developer',
    location: 'USA'
};

let employee = {
    ...person,
    ...job
};

console.log(employee);

In the video, what is the first step that the developer does to pass functions between components?

• He made a function to pass through the objects.

In your own words, what does the increment function do?

• the increment function will go through the objects if the name will be the same it will return as an array and counts again.

How can you pass a method from a parent component into a child component?

• methodName={this.methodName }

How does the child component invoke a method that was passed to it from a parent component?

• this.props.methodName()