Replace a for loop with an Array map()

Question

I have a for loop:

for (let i = 0; i < this.outputList.length; i++) {
  this.outputList[i].checked = this.selectedOutputs.includes(i);
}

Is it posssible to replace this with an array.map? I want to set the 'checked' property of items in the outputList to true if it's index exists in the selectedOutputs array. I can't wrap my head around how this would look using a map function.

Not sensibly. I avoid indexed for loops whenever I can, but I think what you're doing currently is just fine. — CertainPerformance
– CertainPerformance, Commented Nov 25, 2020 at 20:34
map returns an array and i don't think that's what you are looking for — Sifat Haque
– Sifat Haque, Commented Nov 25, 2020 at 20:35
.map is when you want a new array based on a previous one. Since it doesn't seem you're iterating one array and producing another from it, then .map is not a good choice. — VLAZ
– VLAZ, Commented Nov 25, 2020 at 20:36
@noclist please check my reply. I've shared the forEach implementation there — Sifat Haque
– Sifat Haque, Commented Nov 25, 2020 at 20:40

Bergi · Accepted Answer · 2020-11-25 20:39:37Z

3

No, since you are trying to mutate the objects in the outputList instead of building a completely new list, you should not use map. If you just don't like for (let i=0; i<length; i++) loops, you can use for … of:

for (const [i, output] of this.outputList.entries()) {
  output.checked = this.selectedOutputs.includes(i);
}

However, depending on the structure of your selectedOutputs array and assuming that .checked was initialised with false for every output, there might be an even better (and more efficient) approach:

for (const i of this.selectedOutputs) {
  this.outputList[i].checked = true;
}

answered Nov 25, 2020 at 20:39

Bergi

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technophyle · Accepted Answer · 2020-11-25 20:43:19Z

1

You can do it like this:

this.outputList = this.outputList.map((item, i) => ({
  ...item,
  checked: this.selectedOutputs.includes(i),
}));

This will create a new array object from the old array, so it doesn't do the exact same thing. As others mentioned, it's best to use a for iteration in case you shouldn't create a new array object.

edited Nov 25, 2020 at 20:43

answered Nov 25, 2020 at 20:35

technophyle

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Sifat Haque · Accepted Answer · 2020-11-25 20:40:13Z

0

Actually i think forEach is a good match for your purpose. Here you can check the same implementation using forEach.

  this.outputList.forEach((outputList, i) => {
    outputList.checked = this.selectedOutputs.includes(i);
  })

answered Nov 25, 2020 at 20:40

Sifat Haque

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