POJOs

1. Label variables as either Primitive vs. Reference

Javascript considers most data types to be ‘primitive', these data types are immutable, and are passed by value. The more complex data types: Array and Object are mutable, are considered ‘reference' data types, and are passed by reference.

Boolean — Primitive
Null — Primitive
Undefined — Primitive
Number — Primitive
String — Primitive
Array — Reference
Object — Reference
Function — Reference

2. Identify when to use . vs [] when accessing values of an object

    let obj = {"one": 1,"two": 2};// Choose the square brackets property accessor when the property name is determined at// runtime, or if the property name is not a valid identifierlet myKey = "one";
    console.log(obj[myKey]);// Choose the dot property accessor when the property name is known ahead of time.
    console.log(obj.two);

3. Write an object literal with a variable key using interpolation`js

    let keyName = "two";// If the key is not known, you can use an alternative `[]` syntax for// object initialization onlylet obj2 = {[keyName]: 2}
    console.log(obj2);

4. Use the obj[key] !== undefined pattern to check if a given variable that contains a key exists in an object`js

    function  doesKeyExist(obj, key) {// obj[key] !== undefined// or:return key in obj;}```js

    let course = {bootcamp: 'Lambda',course: 'Bootcamp Prep'}
    console.log(doesKeyExist(course, 'course')); // => true
    console.log(doesKeyExist(course, 'name')); // => false

5. Utilize Object`.keys and Object.values in a function`js

    function  printKeys(object) {return Object.keys(object);}```js

    function  printValues(object) {return Object.values(object);}

    console.log(printKeys({dog: "Strelka",dog2: "Belka"}));
    console.log(printValues({dog: "Strelka",dog2: "Belka"}));

6. Iterate through an object using a for in loop`js

    let player = {name: "Sergey",skill: "hockey"};for (let key in player) {
        console.log(key, player[key]);}

    console.log(Object.entries(player));

7. Define a function that utilizes …rest syntax to accept an arbitrary number of arguments`js

    function  restSum(...otherNums) {let sum = 0;
        console.log(otherNums);
        otherNums.forEach(function(num) {
            sum += num;});return sum;}

    console.log(restSum(3, 5, 6)); // => 14
    console.log(restSum(1, 2, 3, 4, 5, 6, 7, 8, 9)); // => 45
    console.log(restSum(0)); // => 0

8. Use …spread syntax for Object literals and Array literals`js

    let numArray = [1, 2, 3];let moreNums = [...numArray, 4, 5, 6]

    console.log(moreNums);```js

    let shoe = {color: "red",size: 10};let newShoe = {...shoe,brand: "Nike",size: 12};
    console.log(newShoe);
    newShoe.color = "black";
    console.log(newShoe);

    console.log(shoe);

9. Destructure an array to reference specific elements`js

    let arr = ['one', 'two', 'three'];```js

    let [first] = arr;
    console.log(first);

10. Destructure an object to reference specific values`js

    let me = {name: "Ian",instruments: ['bass', 'synth', 'guitar'],siblings: {brothers: ['Alistair'],sisters: ['Meghan']}}```js

    let {
        name,instruments: musical_instruments,siblings: {
            sisters
        }} = me;

    console.log(name);
    console.log(musical_instruments);
    console.log(sisters);

11. Write a function that accepts a string as an argument and returns an object representing the count of each character in the array`js

    function  charCount(inputString) {let res = inputString.split("").reduce(function(accum, el) {if (el in accum) {
                accum[el] = accum[el] + 1;} else {
                accum[el] = 1;}return accum;}, {})return res;}

    console.log(charCount('aaabbbeebbcdkjfalksdfjlkasdfasdfiiidkkdingds'));