Javascript Notes - Aug 2019

Go for the cloud, Javascript for the GUI. ReactJs for the framework. Note this stack is aiming to use the language most suitable for the target - ie the native language for that use-case. With as few extra bits or pieces as possible.

So, I’ve learnt Go and I have been using js and Reactjs for a month now, time to make some notes on Javascript.

Values

string, number, boolean, object, function

Objects

Object, Date, Array, String, Number, Boolean

No values

null, undefined

Operators on types

typeof “Anomanda” // returns string

Dates

https://www.w3schools.com/js/js_date_methods.asp

Looping

let myArray= ["one", "two", "three", "four"];
for(let i = 0; i < myArray.length; i++){
  // can use break to exit
}
myArray.forEach(function(element, index) {
  // cannot use break
});
var person = {fname:"John", lname:"Doe", age:25};
var x;
for (x in person) {
  // loop through an object
}
for (x of myArray) {
  //  iterable such as Arrays, Strings, Maps, NodeLists, etc
}
while (i < 10) {
  i++;
}
do { // do it at least once
  i++;
}
while (i < 10);

Object cloning with the spread syntax:

let objClone = {...obj};

Or to clone it, but alter just one field, eg adding 1 to the count field.

let objClone = {...obj, count: obj.count+1 };

Rest syntax for multiple arguments as an arrays

function sum(...theArgs) {
  return theArgs.reduce((prev, curr) => {
      return prev+curr;
    })
}
console.log(sum(1,2,3));

ReactJs

https://itnext.io/react-hooks-context-without-redux-401235df2a68

https://reactjs.org/docs/context.html

https://reactjs.org/docs/hooks-reference.html#usecontext

This is better than any other Hooks guide I’ve seen. It makes it look like the old swing model view controller paradigm.

The reducer is the controller, and the context is the model and the hooks function is the view.

testing

https://jestjs.io/docs/en/getting-started.html

npm install --save-dev jest
npm run test

also, because I have a conflict I have a .env file with

SKIP_PREFLIGHT_CHECK=true

Don’t forget GoLand will also run your Jest tests.