The filtering function does not provide any output

Question

The filtering function does not provide any output

When working in JavaScript, I often find myself needing to filter a list of objects

let dataid = infosStructured.filter(elm => {
  console.log(elm.identifiant);
  console.log("matching value", elm.identifiant == this.dataService.getcurrentId()); // This condition is met
  return elm.identifiant == this.dataService.getcurrentId();
});
console.log(dataid); // However, the result is empty

It's peculiar that even though

elm.identifiant == this.dataService.getcurrentId()

evaluates to true at some point, my dataid remains empty

javascript

Answer 1

Answer №1

There is no correlation with the concept of functional-programming. Check out the following code snippet for clarity:

let f = a => { a == 1 };
f(1); // undefined
let g = a => a == 1;
g(1); // true
let h => a => { return a == 1; };
h(1); // true

Avoid using inlined functions for debugging higher order functions.

Answer 2

There is no correlation with the concept of functional-programming. Check out the following code snippet for clarity:

let f = a => { a == 1 };
f(1); // undefined
let g = a => a == 1;
g(1); // true
let h => a => { return a == 1; };
h(1); // true

Avoid using inlined functions for debugging higher order functions.

Answer 3

Answer №2

When working with multi-line code inside the Array.filter() method, it is necessary to explicitly include the return keyword. However, for single-line code like

infosStructured.filter((elm) => elm)

, the return keyword is not required.

let dataid = infosStructured.filter(elm => {
  console.log(elm.identifiant);
  console.log("matching value", elm.identifiant == this.dataService.getcurrentId()); // I get a true value
  elm.identifiant == this.dataService.getcurrentId();
  return elm;
});
console.log(dataid);

If you do not need the console.log() statements inside the filter, you can simplify it into a one-liner without the return keyword like this:

let dataid = infosStructured.filter((elm) => elm.identifiant == this.dataService.getcurrentId());
console.log(dataid);

Answer 4

When working with multi-line code inside the Array.filter() method, it is necessary to explicitly include the return keyword. However, for single-line code like

infosStructured.filter((elm) => elm)

, the return keyword is not required.

let dataid = infosStructured.filter(elm => {
  console.log(elm.identifiant);
  console.log("matching value", elm.identifiant == this.dataService.getcurrentId()); // I get a true value
  elm.identifiant == this.dataService.getcurrentId();
  return elm;
});
console.log(dataid);

If you do not need the console.log() statements inside the filter, you can simplify it into a one-liner without the return keyword like this:

let dataid = infosStructured.filter((elm) => elm.identifiant == this.dataService.getcurrentId());
console.log(dataid);

The filtering function does not provide any output

Answer №1

Answer №2

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