loop through a javascript array add the value to another array

Question

how to loop through this array , I want to loop and and add name value to an empty array , when I console .log it gives the results below, could you please help , the result of my code is empty array

this.props.names it shows

(3) [{…}, {…}, {…}] 0: {name: "abc", id: 1} 1: {name: "def", id: 2} 2: {name: "gh", id: 3} length: 3 proto: Array(0)

let titles = []
let cats = []
 cats = this.props.names
 let len = this.props.names.length;
 for( i = 0 ;i< cats.length ; i++){
    titles.push(cats[i].id)
 }

return titles;

1< cats.len should be i< cats.length but you can do it more readable with map: const titles=cats.map(cat=>cat.id) — HMR
– HMR, Commented Feb 8, 2019 at 15:23
Try using length instead of len or even better; use the map. — HMR
– HMR, Commented Feb 8, 2019 at 15:26
could you please post some data samples ? EX : this.props.names=[a,b,c,d] and the expected and current result Expected result:[x,y,z]; current result : [e,r,t] — RegularGuy
– RegularGuy, Commented Feb 8, 2019 at 15:27
You could basically replace all the code posted here with return this.props.names.map(cat=>cat.id) — HMR
– HMR, Commented Feb 8, 2019 at 15:28

RegularGuy · Accepted Answer · 2019-02-08 15:38:37Z

1

from what i see... do

let titles = []
let cats = [{name: "abc", id: 1},{name: "def", id: 2},{name: "gh", id: 3}]
 for( var p = 0 ;p< cats.length ; p++){
    titles.push(cats[p].id)
 }

console.log(titles)

edited Feb 8, 2019 at 15:38

answered Feb 8, 2019 at 15:28

RegularGuy

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RegularGuy Over a year ago

added snippet .

jo_va · Accepted Answer · 2019-02-08 15:51:12Z

0

If you simply want to extract the ids, and props and/or names may be empty or null, you can do it using map:

const titles = (props && props.names || []).map(val => val.id);

Here props && props.names || [] will be equal to [] if props or props.names evaluates to falsy. That way, you can still apply map to it, which will return an empty array in this case.

function demo(props) {
  const titles = (props && props.names || []).map(val => val.id);
  console.log(titles);
}

demo({ names: [{name: 'one', id: 1}, {name: 'two', id: 2}, {name: 'three', id: 3}] });
demo({ names: [] });
demo({});
demo(null);

See the MDN doc about the map operator.

edited Feb 8, 2019 at 15:51

answered Feb 8, 2019 at 15:43

jo_va

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Heretic Monkey Over a year ago

How would this help if props is empty?

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