2019-02-27 FEB

JS Objects

Collection of "properties," or "key-value" pairs.
Instantiate Object: obj = {};
Create object: user = {'name':'Joseph', 'age':49, 'dept':'BMI', }
- Conventions
  - Trailing Commas;
  - Space between opening bracket and first element; space between closing bracket and last element;
  - JS allows you to omit quotes when the keys contain only non-space characters
Create array of objects; Using array methods to access object properties
- ua = [{name: 'Joe', age: 40}, {name: 'Eileen', age: 25}]
- ua.forEach((x) => {console.log('Name: ' + x.name + '\n' + 'Age: ' + x.age);})
Modifying and Assigning Object Properties; Filtering based on Object Property
- projectObj1 = { 'name':'U12', 'lead':'MrU', 'status':under budget, ahead of schedule', }
- ua[0].proj = projectObj;
  - Will overwrite property if key exists, create new property if key does not exist.
- projectObj2 = {'name':'docminer', 'lead':'Hasit', 'status':'a-ok'}
- ua[1].proj = projectObj2;
- ua.filter( (x) => ( x.proj.name == 'U24') );
Copying a javascript object:
- From https://flaviocopes.com/how-to-clone-javascript-object/:
  - "A shallow copy successfully copies primitive types like numbers and strings, but any object reference will not be recursively copied, but instead the new, copied object will reference the same object."
- To perform a deep copy, use the spread operator ( ... ): the following deep-copies contents of user to the new variable user2:

var x =5; // "declaration and assignment; a.k.a. initialization"

x=4; // "re-assignment"

Variables declared with "const" cannot be reassigned.

The following won't work because const y, assigned to 10, is being reassigned:

const y = 10;

y=5

The following will work, because const z, assigned to [1,2,3], is not being reassigned; the array it's pointing to ie being modified.

const z = [1,2,3];

z[0] = 3; // z is now [3,2,3]

Joe-approved comparison table:

Functions

Traditional Way (Factorial):

function factorial(x) {

if (x <=1 ) {return(1)}

else {return(x*factorial(x-1))}

}

ES6 Way: // Good practice to use "const" whenever possible

const fac = (x) => ( (x<=1) ? 1 : x *fac(x-1) )

const factorial = (x) => { return (x<=1) ? 1 : x *fac(x-1)}

Decrement:

for(n=100;n>0;n--) {console.log(n)}

Increment:

for(i=0;i<100;i++) {console.log(i)}

Evens and Odds:

for(i=0; i<=10;i+=2) {console.log(i)}