Javascript variable from for loop does not get called in push method

Question

I tried doing items.map((item) => arrs.push({item._id:item.word})); but the first element for the key did not work at all so I instead wrote a basic for loop. Now creating the for loop works fine and console logging arrs after the loop shows the correct information for the values but the keys for all of them show "temp" as a string, instead of the desired id from items[i]._id. In VS code the temp in let temp=item... is greyed out and says "temp is declared but its value is never read". Now if I put a console.log(temp) between let temp... and arrs.push... it correctly logs out the value in the temp variable.

 const arrs = [];
  for (let i = 0; i < items.length; i++) {
    let temp = items[i]._id;
    arrs.push({ temp: items[i].word });
  }

I thought temp was within the same scope so it should work. Have no idea what is happening.

I tried creating different scopes but nothing worked.

Basically wanting to do this `arrs.push({ items[i]._id: items[i].word });` . Yet I cannot do this directly causes and error saying expected `:` or `,`. It seems that only the key causes the error if I get rid of the key and leave the value it works fine. So I wanted to create a temp variable setting the value to `items[i]._id` as a way to see if the error goes away. Yet now with setting the temp var as a key it cannot read it. — tester0001, Mar 27 '22 at 04:31

Nolan B. · Accepted Answer · 2022-03-27T04:40:41.190

You're declaring the property name to be "temp", not assigning it as a value. If you're trying to make a property name be the value of temp, you can use a computed property name by surrounding it with square brackets [].

const arrs = [];
for (let i = 0; i < items.length; i++) {
  arrs.push({[items[i]._id]: items[i].word});
}

This will create an object with a key items[i]._id and value items[i].word. Better yet, you can use map:

const arrs = items.map(item => { return {[item._id]: item.word}});

score 0 · Answer 2 · answered Mar 27 '22 at 04:36

Follow this code snippet, created an object and pushing them in arrs in loop:

 let items = [
            {_id:'1',
                word:'test'
            },
            {_id:'2',
                word:'test2'
            },
            {_id:'3',
                word:'test3'
            },
            {_id:'4',
                word:'test4'
            }
            ];

    let arrs = [];        
    for (var i = 0; i < items.length; i++){
      var obj = {
          [items[i]._id] : items[i].word
      }
      arrs.push(obj);
    }



    console.log(arrs)

 let items = [
            {_id:'1',
                word:'test'
            },
            {_id:'2',
                word:'test2'
            },
            {_id:'3',
                word:'test3'
            },
            {_id:'4',
                word:'test4'
            }
            ];

    let arrs = [];        
    for (var i = 0; i < items.length; i++){
      var obj = {
          [items[i]._id] : items[i].word
      }
      arrs.push(obj);
    }

    console.log(arrs)

Javascript variable from for loop does not get called in push method

2 Answers2