Retrieving the value of array which is returned as string

Question

I have the following array stored at the front end.

myArr[0] = new Array("AF", "B", "C", "D", "EM", "F", "G", "H", "I", "J");
myArr[1] = new Array("C", "DD", "M", "ED", "F", "DG", "B", "C", "D", "C");
myArr[2] = new Array("F", "G", "H", "I", "E", "F", "G", "H", "I", "J");

i need to get the value of the elements in an array. for example myArr[0][0] should return AF. unfortunately i am getting the position to be find of the array as string of array as follows from a service call.

["myArr[1][6]", "myArr[3][4]", "myArr[4][2]"]

how do i convert this and get the value at the array positions mentioned above. Thanks in advance.

Is the service that you call something you can amend? The response isn't ideal. You'd be better receiving the positions instead. — Adrian, Jul 11 '19 at 10:26
Possible duplicate of [Accessing nested JavaScript objects with string key](https://stackoverflow.com/questions/6491463/accessing-nested-javascript-objects-with-string-key) — adiga, Jul 11 '19 at 10:32

Will Jenkins · Answer 1 · 2019-07-11T10:49:24.980

3

You can use eval to execute strings as script:

eval("myArr[1][6]") // gives "C"

See codepen here: https://codepen.io/jenko3000/pen/NZJRYK

Be careful though, executing strings as scripts is dangerous.

edited Jul 11 '19 at 10:49

answered Jul 11 '19 at 10:25

Will Jenkins

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why the downvote? this is totally acceptable if it's safe to do it – Will Jenkins Jul 11 '19 at 10:31
Why did you post a codepen? Couldn't you use a stack snippet? – Kobe Jul 11 '19 at 10:32
I guess, I just find codepens easier to work with. The snippets are horribly clunky. – Will Jenkins Jul 11 '19 at 10:32
They can be, but the downsides to a codepen are that you have to open a new page and open up devtools to check the console. – Kobe Jul 11 '19 at 10:33
True enough... swings and roundabouts eh – Will Jenkins Jul 11 '19 at 10:34
1

Haha, exactly :P – Kobe Jul 11 '19 at 10:34
@WillJenkins Can you edit your answer? I down-voted your answer by accident it seems. There was one above yours (or below) that was complete nonsense. Not sure how I went for both of them. Sorry dude! – Adrian Jul 11 '19 at 10:42
just added a link to mdn - that sort of thing? – Will Jenkins Jul 11 '19 at 10:49
1

@WillJenkins Awesome, that's me removed my -1. Sorry again. I wanted you to edit it because 10 minutes elapsed and my vote was locked until you edited. – Adrian Jul 11 '19 at 10:57

score 1 · Answer 2 · edited Jul 11 '19 at 10:30

You can use regex to "extract" the two indices and then use them to get the values like so:

let myArr = [];
myArr[0] = new Array("AF", "B", "C", "D", "EM", "F", "G", "H", "I", "J");
myArr[1] = new Array("C", "DD", "M", "ED", "F", "DG", "B", "C", "D", "C");
myArr[2] = new Array("F", "G", "H", "I", "E", "F", "G", "H", "I", "J");

let arr = ["myArr[1][6]", "myArr[2][4]", "myArr[0][2]"];

let res = arr.map(str => {
  let [x, y] = str.match(/(\d+)/g);
  return myArr[x][y];
});
console.log(res);

score 1 · Answer 3 · edited Jun 20 '20 at 09:12

There's no need to over-complicate the issue. A simple map over each value and evaluate will suffice:

const myArr = [
  ["AF", "B", "C", "D", "EM", "F", "G", "H", "I", "J"],
  ["C", "DD", "M", "ED", "F", "DG", "B", "C", "D", "C"],
  ["F", "G", "H", "I", "E", "F", "G", "H", "I", "J"]
]

var positions = ["myArr[1][6]", "myArr[2][4]", "myArr[0][2]"]

positions = positions.map(eval)

console.log(positions)

Note, we can use the shorthand .map(eval) over .map(e => eval(e)) because we are only passing one element to one function, so the shorthand will do that for us.

Also, as Will pointed out, eval can be dangerous, as eval can execute malicious scripts.

Ajanyan Pradeep · Answer 4 · 2019-07-11T10:53:03.767

This code will replace the positions stored in the array with their respective values.

let myArr=[]
myArr[0] = new Array("AF", "B", "C", "D", "EM", "F", "G", "H", "I", "J");
myArr[1] = new Array("C", "DD", "M", "ED", "F", "DG", "B", "C", "D", "C");
myArr[2] = new Array("F", "G", "H", "I", "E", "F", "G", "H", "I", "J");
let values=["myArr[1][6]", "myArr[2][4]", "myArr[0][2]"];
for (var i = 0; i < values.length; i++)
{
  values[i]=eval(values[i])
}
console.log(values)

Retrieving the value of array which is returned as string

4 Answers4