CODEWITHSUNDEEP
javascriptarrayscallbackmaps
Awash
Awash

Reputation: 29

JavaScript Map Array

array called 'notes' contains 5 objects , each object has keys

var notes = [
   {
       title: "Home",
       message: "is a good story",
       status: 'new',
       author:"dala",
   },
   {
       title: "School",
       message: "Have to go everday",
       status: 'new',
       author:"aisha",
   },
   {
       title: "study",
       message: "we have exam to pass",
       status: 'new',
       author:"Omar",
   },
   {
       title: "Work",
       message: "dead line is close",
       status: 'new',
       author:"Said",
   },
   {
       title: "homework",
       message: "as today we need to do it",
       status: 'new',
       author:"Amal",
   },
];

i want to update all the notes's status to be 'completed', the error is the code only update the first Object

function map(notes,callback){
   const newNotes =[];
   for(var i=0; i<notes.length; i++) {
       const result = callback(notes[i].status = "completed",i);
       newNotes.push(result);
       return newNotes;
   }
}
var outp = map(notes,function(value, i){
   console.log(i)
   for(var a= 0; a<value.length; a++){
       return notes;

   }

})
console.log(outp);

I was training on the callback function, and this training code was the face of a problem writing the code If you have useful resources to learn from, please share them with me

Upvotes: 0

Views: 663

Answers (2)

Vincent Menzel
Vincent Menzel

Reputation: 1055

In the map function you returned the newNotes array within the for loop instead of after it. However I would suggest to use the built in map function.

var notes = [
   {
       title: "Home",
       message: "is a good story",
       status: 'new',
       author:"dala",
   },
   {
       title: "School",
       message: "Have to go everday",
       status: 'new',
       author:"aisha",
   },
   {
       title: "study",
       message: "we have exam to pass",
       status: 'new',
       author:"Omar",
   },
   {
       title: "Work",
       message: "dead line is close",
       status: 'new',
       author:"Said",
   },
   {
       title: "homework",
       message: "as today we need to do it",
       status: 'new',
       author:"Amal",
   },
];

function map(notes,callback){
   const newNotes =[];
   for(var i=0; i<notes.length; i++) {
       const result = callback(notes[i].status = "completed",i);
       newNotes.push(result);
   }
   return newNotes;
}
var outp = map(notes,function(value, i){
   console.log(i)
   for(var a= 0; a<value.length; a++){
       return notes;
   }
})
console.log(outp);

Upvotes: 1

T.J. Crowder
T.J. Crowder

Reputation: 1074138

You don't need to write your own map function, Array.prototype.map already does what your map function does (and a bit more, but that's not relevant).

The problem is:

  • Your map does return newNotes; inside the for loop, so it returns when the loop has only done one of the elements.
  • map isn't calling your callback correctly.
  • Your callback isn't doing what the map function expects it to.

The call to your callback should be just:

const result = callback(notes[i], i);

And the return newNotes; should be after the loop.

Then your callback should create a new object with the properties from the original object passed in, plus status: "completed" — perhaps using an object literal with spread syntax, like this:

const output = map(notes, function(note, index) {
    return {...note, status: "completed" };
});

Upvotes: 2

Related Questions