JavaScript Map Array

Question

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

It wrong to use notes[i].status = "completed" in your callback argument. — TropicsCold
– TropicsCold, Commented Jan 11, 2022 at 8:07

T.J. Crowder · Accepted Answer · 2022-01-11 08:06:15Z

2

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" };
});

answered Jan 11, 2022 at 8:06

T.J. Crowder

1.1m201 gold badges2k silver badges2k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

TropicsCold Over a year ago

I consider he/she is doing practice of callback function?

T.J. Crowder Over a year ago

@TropicsCold - They've said that's what they're doing, which is why I didn't tell them to just use Array.prototype.map. :-)

Vincent Menzel · Accepted Answer · 2022-01-11 08:09:26Z

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);

Collectives™ on Stack Overflow

JavaScript Map Array

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related