HTML and JS

If you want to clear something after you insert an input value; set inputtext.value = ''
If you want elements like buttons/images to appear on different line in HTML, <div> to separate into lines 
If you want to change certain index, you can access it like changeTodoPositionInput.value but .value will return string; but you can do .valueAsNumber, to make it number
  changeTodo: function(){
    var changeTodoPositionInput = document.getElementById('changeTodoPositionInput')
    var changeTodoTextInput = document.getElementById('changeTodoTextInput')
    todoList.changeTodo(changeTodoPositionInput.valueAsNumber, changeTodoTextInput.value)
  }
  
  One method of listing <ul><li></li></ul>
  document.querySelector(''). Create <ul></ul> in HTML, declare var in console (e.g. var ul =  document.querySelector('ul'))if hover over it in console, it will highlight
  document.createElement(''). for e.g. var li = document.createElement('li'). 
  then ul.appendChild('li')

Javascript

for (let i of array) - value
for (let i in array) - index

**************
This when console.log(obj of any array) will return getIndexBy;
Array.prototype.getIndexBy = function (name, value) {       
  for (var i = 0; i < this.length; i++) {
    if (this[i][name] === value) {
      return i
    }
  }
  return 'No such value'
}
Instead, we can declare the enum to false;
Object.defineProperty(Array.prototype, 'getIndexBy', {
  enumerable: false,
  value: function (name, value) {
    for (var i = 0; i < this.length; i++) {
      if (this[i][name] === value) {
        return i
      }
    }
  }
})

***Arguments vs parameters***
The formal parameter is what's given in the function declaration/definition/prototype,
the actual argument is what's passed when calling the function, an instance of a formal parameter
int foo(int x, int y) { -> paramaters
    ...
}
foo(5, z); -> 5 and z are the actual arguments 

***forEach**
[1,2,3].forEach(function(){   
 console.log('hi')
})

= forEach([1,2,3], function(){
   console.log('hi')
})

**function within function**
function a(){
  return 'a'
}

//if u do this, you will get 'undefined'
function b(){
 a()
}
//But if you do this, you will get the result
functon b(){
 return a()
}