Question about using the map method in Javascript to generate an array with undefined elements

Question

Question about using the map method in Javascript to generate an array with undefined elements

I've been attempting to utilize the .map method in order to create a new array named workspaces, containing only the ids from the existing array. However, despite the console.log() displaying the ids as expected, the return statement does not populate the workspaces array with these ids.

    const workspaces = this.networkTree.map( (group) => {
      group.units.map( (unit) => {
        console.log(unit.id);   // The id is correctly displayed in the console e.g '12345'
        return unit.id;
      });
    });

    console.log(workspaces);   // Each sub-array within workspaces appears empty (referenced image below)

https://i.sstatic.net/GQHZb.png

javascript arrays dictionary

Answer 1

Answer №1

To ensure you get the desired result, make sure to return the result from the nested map function, as shown below:

const workspaces = this.networkTree.map((group) => {
  return group.units.map((unit) => { // <= remember to include the `return` statement here
    console.log(unit.id);
    return unit.id;
  });
});

console.log(workspaces);

Another approach would be to skip using braces for the inline function like this:

const workspaces = this.networkTree.map((group) => 
  group.units.map((unit) => {
    console.log(unit.id);
    return unit.id;
  })
);

If you decide to eliminate the console.log, you can simplify it further:

const workspaces = this.networkTree.map((group) => group.units.map((unit) => unit.id));

Answer 2

To ensure you get the desired result, make sure to return the result from the nested map function, as shown below:

const workspaces = this.networkTree.map((group) => {
  return group.units.map((unit) => { // <= remember to include the `return` statement here
    console.log(unit.id);
    return unit.id;
  });
});

console.log(workspaces);

Another approach would be to skip using braces for the inline function like this:

const workspaces = this.networkTree.map((group) => 
  group.units.map((unit) => {
    console.log(unit.id);
    return unit.id;
  })
);

If you decide to eliminate the console.log, you can simplify it further:

const workspaces = this.networkTree.map((group) => group.units.map((unit) => unit.id));

Answer 3

Answer №2

Ensure you include a return statement in your code:

const workspaces = this.networkTree.map((group) => {
    return group.units.map((unit) => {
        return unit.id;
    });
});

Alternatively, considering the use of arrow functions:

const workspaces = this.networkTree.map((group) => group.units.map((unit) => unit.id));

Answer 4

Ensure you include a return statement in your code:

const workspaces = this.networkTree.map((group) => {
    return group.units.map((unit) => {
        return unit.id;
    });
});

Alternatively, considering the use of arrow functions:

const workspaces = this.networkTree.map((group) => group.units.map((unit) => unit.id));

Answer 5

Answer №3

The issue may be stemming from your failure to include the new unit within the return statement of the outer map function. One potential solution could involve replacing the curly braces with parentheses in the outer map function for an auto return effect.

const workspaces = this.networkTree.map( (group) => ( // using (
      group.units.map( (unit) => {
        console.log(unit.id); 
        return unit.id;
      });
    )); // closing )

Answer 6

The issue may be stemming from your failure to include the new unit within the return statement of the outer map function. One potential solution could involve replacing the curly braces with parentheses in the outer map function for an auto return effect.

const workspaces = this.networkTree.map( (group) => ( // using (
      group.units.map( (unit) => {
        console.log(unit.id); 
        return unit.id;
      });
    )); // closing )

Question about using the map method in Javascript to generate an array with undefined elements

Answer №1

Answer №2

Answer №3

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