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How to Edit Todo List Without Using Global Variables Functional Programming Vanilla JS

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0

How do you continually edit an array of todos while using FP? I understand that when you use array methods such as .concat() you are returning a copy of the array and not editing the original. Here is my original code that simply pushes a new todo to the todo array. This permanently changes the myTodos variable which we are trying to avoid.

let myTodos = []

function addTodo(newTodo) 
 myTodos.push(newTodo)
 return myTodos

I have rewritten this function as such:

const addTodo = (arr, todoText) => arr.concat(todoText)

This works just fine but I don't understand how to keep the value that is returned when I am supposed to avoid global variables. If I call this to add a second todo to my list it will only return that second todo since the var is not being stored anywhere. I feel like there is a very obvious way to work this but I just cannot seem to figure it out.

My apologies I am still very new to the programming world. Any help would be greatly appreciated.

javascript arrays functional-programming concat

share|improve this question

edited Mar 8 at 1:56

KwMarkHintz

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Uh, no, push and pop alter the original array
  
  – Taplar
  Mar 8 at 1:54
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  You literally have zero reason to make a wrapper method around the push method, with what you are doing. Just push to your array
  
  – Taplar
  Mar 8 at 1:56
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Taplar - probably homework assignment - must be functional
  
  – Randy Casburn
  Mar 8 at 1:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  But it's not functional, because it's being over complicated, :)
  
  – Taplar
  Mar 8 at 1:57
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Taplar - agree completely.
  
  – Randy Casburn
  Mar 8 at 1:59
  

  
  
  
  

 | 
show 4 more comments

0

How do you continually edit an array of todos while using FP? I understand that when you use array methods such as .concat() you are returning a copy of the array and not editing the original. Here is my original code that simply pushes a new todo to the todo array. This permanently changes the myTodos variable which we are trying to avoid.

let myTodos = []

function addTodo(newTodo) 
 myTodos.push(newTodo)
 return myTodos

I have rewritten this function as such:

const addTodo = (arr, todoText) => arr.concat(todoText)

This works just fine but I don't understand how to keep the value that is returned when I am supposed to avoid global variables. If I call this to add a second todo to my list it will only return that second todo since the var is not being stored anywhere. I feel like there is a very obvious way to work this but I just cannot seem to figure it out.

My apologies I am still very new to the programming world. Any help would be greatly appreciated.

javascript arrays functional-programming concat

share|improve this question

edited Mar 8 at 1:56

KwMarkHintz

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Uh, no, push and pop alter the original array
  
  – Taplar
  Mar 8 at 1:54
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  You literally have zero reason to make a wrapper method around the push method, with what you are doing. Just push to your array
  
  – Taplar
  Mar 8 at 1:56
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Taplar - probably homework assignment - must be functional
  
  – Randy Casburn
  Mar 8 at 1:57
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  But it's not functional, because it's being over complicated, :)
  
  – Taplar
  Mar 8 at 1:57
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @Taplar - agree completely.
  
  – Randy Casburn
  Mar 8 at 1:59
  

  
  
  
  

 | 
show 4 more comments

How do you continually edit an array of todos while using FP? I understand that when you use array methods such as .concat() you are returning a copy of the array and not editing the original. Here is my original code that simply pushes a new todo to the todo array. This permanently changes the myTodos variable which we are trying to avoid.

let myTodos = []

function addTodo(newTodo) 
 myTodos.push(newTodo)
 return myTodos

I have rewritten this function as such:

const addTodo = (arr, todoText) => arr.concat(todoText)

This works just fine but I don't understand how to keep the value that is returned when I am supposed to avoid global variables. If I call this to add a second todo to my list it will only return that second todo since the var is not being stored anywhere. I feel like there is a very obvious way to work this but I just cannot seem to figure it out.

My apologies I am still very new to the programming world. Any help would be greatly appreciated.

javascript arrays functional-programming concat

share|improve this question

edited Mar 8 at 1:56

KwMarkHintz

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

let myTodos = []

function addTodo(newTodo) 
 myTodos.push(newTodo)
 return myTodos

const addTodo = (arr, todoText) => arr.concat(todoText)

share|improve this question

edited Mar 8 at 1:56

KwMarkHintz

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

share|improve this question

edited Mar 8 at 1:56

KwMarkHintz

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

asked Mar 8 at 1:53

KwMarkHintzKwMarkHintz

166

1 Answer
1

active

oldest

votes

1

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

share|improve this answer

answered Mar 8 at 2:15

TaplarTaplar

18k21529

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you! This is exactly what I was looking for. I was under the impression that using a new variable to store the array was impure.
  
  – KwMarkHintz
  Mar 8 at 4:16
  

  
  
  
  

add a comment | 

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1

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

share|improve this answer

answered Mar 8 at 2:15

TaplarTaplar

18k21529

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you! This is exactly what I was looking for. I was under the impression that using a new variable to store the array was impure.
  
  – KwMarkHintz
  Mar 8 at 4:16
  

  
  
  
  

add a comment | 

1

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

share|improve this answer

answered Mar 8 at 2:15

TaplarTaplar

18k21529

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you! This is exactly what I was looking for. I was under the impression that using a new variable to store the array was impure.
  
  – KwMarkHintz
  Mar 8 at 4:16
  

  
  
  
  

add a comment | 

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

share|improve this answer

answered Mar 8 at 2:15

TaplarTaplar

18k21529

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

/*
1) how to avoid global variables?
2) how to not change the original?
3) how to keep the changed

#1 - this is called an Immediately Invoked Functional Expression (IIFE for short)
 What this does is lets us create a "scope" within our script. Variables we
 create inside it with `var` or `let` or `const`, are not global. They will
 only exist inside the scope.
*/
 (function()
 var originalArray = [];
 // #2 - concat does not change the original array
 // #3 - to keep the change, just store it in another variable
 var changedArray = originalArray.concat('me');
 
 // #3 - if I want to make more changes, I use the new variable
 changedArray = changedArray.concat('yet another value');
 
 console.log(originalArray);
 console.log(changedArray);
 ());

share|improve this answer

answered Mar 8 at 2:15

TaplarTaplar

18k21529

answered Mar 8 at 2:15

TaplarTaplar

18k21529

answered Mar 8 at 2:15

TaplarTaplar

18k21529